Specify padding/margin for -tterm.

This adds initial support (which will be refactored in subsequent
commits) for specifying both --term-hmargin and --term-hpadding.
The former will move the content to the right; the latter will pad
into the content width toward the right.

In doing so, make the default body padding to be zero, which allows
the users to control finely for horizontal indent.

Fixes #129

lowdown.h

@@ -320,6 +320,7 @@ struct	lowdown_opts {
 	size_t			  maxdepth;
 	size_t			  cols;
 	size_t			  hmargin;
+	size_t			  hpadding;
 	size_t			  vmargin;
 	unsigned int		  feat;
 #define LOWDOWN_ATTRS		  0x80000

main.c

@@ -321,6 +321,7 @@ main(int argc, char *argv[])
 
 		{ "term-columns",	required_argument, NULL, 4 },
 		{ "term-hmargin",	required_argument, NULL, 2 },
+		{ "term-hpadding",	required_argument, NULL, 9 },
 		{ "term-vmargin",	required_argument, NULL, 3 },
 		{ "term-width",		required_argument, NULL, 1 },
 
@@ -426,6 +427,7 @@ main(int argc, char *argv[])
 	TAILQ_INIT(&mq);
 	memset(&opts, 0, sizeof(struct lowdown_opts));
 
+	opts.hpadding = 4;
 	opts.maxdepth = 128;
 	opts.type = LOWDOWN_HTML;
 	opts.feat =
@@ -571,6 +573,12 @@ main(int argc, char *argv[])
 		case 8:
 			templfn = optarg;
 			break;
+		case 9:
+			opts.hpadding = strtonum
+				(optarg, 0, INT_MAX, &er);
+			if (er == NULL)
+				break;
+			errx(1, "--term-hpadding: %s", er);
 		default:
 			goto usage;
 		}

regress/table-footnotes.term

@@ -1,18 +1,18 @@
     This used to crash -Tterm because the footnote size was saved and
-    zeroed prior to table column-width scanning, then restored. However,
-    this could result in off-by-ones or -twos because the actual
-    footnotes may have gone double-digit while the zeroed wouldn’t.
-
+    zeroed prior to table column-width scanning, then restored.
+    However, this could result in off-by-ones or -twos because the
+    actual footnotes may have gone double-digit while the zeroed wouldn’t.
+    
     a[1] a[2] a[3] a[4] a[5] a[6] a[7] a[8]
-
+    
               Officer | Rank                
     ------------------|----------------------
       Jean-Luc Picard | Captain             
               Worf[9] | Lieutenant Commander
              Data[10] | Lieutenant Commander
     William Riker[11] | Commander           
 
-    ~~~~~~~~
+    ~~~~~~~~
 
      1. foo
      2. foo

regress/term-width.md

@@ -0,0 +1,14 @@
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***testttt***
+***test***

regress/term-width.term

@@ -0,0 +1,2 @@
+    test test test test test test test test test test test test testttt
+    test

regress/term-width2.md

@@ -0,0 +1,14 @@
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***testtttt***
+***test***

regress/term-width2.term

@@ -0,0 +1,2 @@
+    test test test test test test test test test test test test 
+    testtttt test

regress/term-width3.md

@@ -0,0 +1,12 @@
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***
+***test***                     ***testttt***

regress/term-width3.term

@@ -0,0 +1 @@
+    test test test test test test test test test test test test testttt

term.c

@@ -45,6 +45,7 @@ struct term {
 	size_t			  stackpos; /* position in stack */
 	size_t			  maxcol; /* soft limit */
 	size_t			  hmargin; /* left of content */
+	size_t			  hpadding; /* left of content */
 	size_t			  vmargin; /* before/after content */
 	struct lowdown_buf	 *tmp; /* for temporary allocations */
 	wchar_t			 *buf; /* buffer for counting wchar */
@@ -619,6 +620,9 @@ rndr_buf_startline_prefixes(struct term *term,
 		for (i = 0; i < term->hmargin; i++)
 			if (!HBUF_PUTSL(out, " "))
 				return 0;
+		for (i = 0; i < term->hpadding; i++)
+			if (!HBUF_PUTSL(out, " "))
+				return 0;
 		break;
 	case LOWDOWN_BLOCKQUOTE:
 		rndr_node_style_apply(&sinner, &sty_bkqt_pfx);
@@ -1718,10 +1722,18 @@ lowdown_term_new(const struct lowdown_opts *opts)
 	if (opts != NULL) {
 		st->maxcol = opts->cols == 0 ? 80 : opts->cols;
 		st->hmargin = opts->hmargin;
+		st->hpadding = opts->hpadding;
 		st->vmargin = opts->vmargin;
 		st->opts = opts->oflags;
-	} else
+	} else {
 		st->maxcol = 80;
+		st->hpadding = 4;
+	}
+
+	if (st->hpadding >= st->maxcol)
+		st->maxcol = 1;
+	else
+		st->maxcol -= st->hpadding;
 
 	if ((st->tmp = hbuf_new(32)) == NULL) {
 		free(st);

term.h

@@ -164,7 +164,7 @@ static const struct sty sty_table =	{ 0, 0, 0, 0,   0, 93, 0 };
  */
 
 /* All non-header (child to the document root) content (no style). */
-static const struct pfx pfx_body =	{ "    ", 4 };
+static const struct pfx pfx_body =	{ "", 0 };
 
 /* All header (child to the document root) content (no style). */
 static const struct pfx pfx_header =	{ "", 0 };