dcmp_*: fix python-rsrcfork links and replace with permalinks

Old links broke after restructuring in python-rsrcfork repo. See:
#303 (comment)

macos/resource_compression/dcmp_0.ksy

@@ -34,7 +34,7 @@ doc: |
 
   The `'dcmp' (1)` compression format (see dcmp_1.ksy) is very similar to this format,
   with the main difference that it operates mostly on single bytes rather than two-byte units.
-doc-ref: 'https://github.com/dgelessus/python-rsrcfork/tree/master/rsrcfork/compress/dcmp0.py'
+doc-ref: 'https://github.com/dgelessus/python-rsrcfork/blob/f891a6ee003b094bf4fc570832f90190260d795b/src/rsrcfork/compress/dcmp0.py'
 seq:
   - id: chunks
     type: chunk

macos/resource_compression/dcmp_1.ksy

@@ -31,7 +31,7 @@ doc: |
   The `'dcmp' (0)` format also appears to be generally preferred over `'dcmp' (1)`,
   with the latter only being used in resource files that contain mostly unaligned data,
   such as text.
-doc-ref: 'https://github.com/dgelessus/python-rsrcfork/tree/master/rsrcfork/compress/dcmp1.py'
+doc-ref: 'https://github.com/dgelessus/python-rsrcfork/blob/f891a6ee003b094bf4fc570832f90190260d795b/src/rsrcfork/compress/dcmp1.py'
 seq:
   - id: chunks
     type: chunk

macos/resource_compression/dcmp_2.ksy

@@ -27,7 +27,7 @@ doc: |
   which allows using two-byte literals in addition to single-byte table references,
   at the cost of requiring an extra "tag" byte every 16 output bytes,
   to differentiate literals and table references.
-doc-ref: 'https://github.com/dgelessus/python-rsrcfork/tree/master/rsrcfork/compress/dcmp2.py'
+doc-ref: 'https://github.com/dgelessus/python-rsrcfork/blob/f891a6ee003b094bf4fc570832f90190260d795b/src/rsrcfork/compress/dcmp2.py'
 params:
   - id: len_decompressed
     type: u4

macos/resource_compression/dcmp_variable_length_integer.ksy

@@ -24,7 +24,7 @@ doc: |
   In practice,
   values are always stored in the smallest possible format,
   but technically any of the larger formats could be used as well.
-doc-ref: 'https://github.com/dgelessus/python-rsrcfork/tree/master/rsrcfork/compress/common.py'
+doc-ref: 'https://github.com/dgelessus/python-rsrcfork/blob/f891a6ee003b094bf4fc570832f90190260d795b/src/rsrcfork/compress/common.py'
 seq:
   - id: first
     type: u1