Better documentation and docs search for punctuation

[mbauman]

This tries to make documentation for Julia's punctuation and obscure syntaxes a bit more discoverable. Adds keyword doc strings for things like { and [, updates the punctuation chapter of the documentation to include the names of the punctuation characters so its more searchable, and adds a whole slew of cross-links between everything.

I also got sniped into re-writing a bit of the array literal section of the array manual.

Here's one example. Before:

help?> {}
ERROR: LoadError: BoundsError: attempt to access 0-element Array{Any,1} at index [1]
Stacktrace:
 [1] getindex at ./array.jl:728 [inlined]
 [2] astname(::Expr, ::Bool) at ./docs/Docs.jl:287
 [3] namify at ./docs/Docs.jl:277 [inlined]
 [4] lookup_doc(::Expr) at /Users/mbauman/Julia/release-1.2/usr/share/julia/stdlib/v1.2/REPL/src/docview.jl:137
 [5] docm(::LineNumberNode, ::Module, ::Any) at ./docs/Docs.jl:501
 [6] @doc(::LineNumberNode, ::Module, ::Expr, ::Vararg{Expr,N} where N) at ./boot.jl:461
in expression starting at /Users/mbauman/Julia/release-1.2/usr/share/julia/stdlib/v1.2/REPL/src/docview.jl:349

After:

help?> {}
search:

  {}

  Curly braces are used to specify type parameters.

  Type parameters allow a single type declaration to introduce a whole family of new types — one for each possible
  combination of parameter values. For example, the Set type describes many possible types of sets; it uses one type
  parameter to describe the type of the elements it contains. The specific parameterized types Set{Float64} and
  Set{Int64} describe two concrete types: both are subtypes (<:) of Set, but the former has Float64 elements and the
  latter has Int64 elements.

[StefanKarpinski]

What's required to make progress here? This is a great improvement.

[mbauman]

I just need to figure out how to make all those cross-links. I poked at it for a little bit but made no progress. I'll try again this afternoon.

[mbauman]

Hm, I tried all possible combinations of @ref Base.:! / @ref !(x) / @ref Base.!(x) / etc that I could think of and none of them worked. Perhaps this isn't possible at the moment? I'll just move the link over into the left-hand column for now — the auto link on [`!`](@ref) does work as expected.

[StefanKarpinski]

Who might know how to do this? @mortenpi maybe?

[mbauman]

I think the relevant issue is JuliaDocs/Documenter.jl#781 — that is, it's not possible at the moment.

[mbauman]

Test failures are now unrelated. Anything else here?