Many LaTeX backend fixes

After this commit, we can run with `--latex` on all boot libraries
without crashing (although the generated LaTeX still fails to compile in
a handful of larger packages like `ghc` and `base`).

 * Add newlines after all block elements in LaTeX. This is important to
   prevent the final output from being more an more indented. See the
   `latext-test/src/Example` test case for a sample of this.

 * Support associated types in class declarations (but not yet defaults)

 * Several small issues for producing compiling LaTeX;
     - avoid empy `\haddockbeginargs` lists (ex: `type family Any`)
     - properly escape identifiers depending on context (ex: `Int#`)
     - add `vbox` around `itemize`/`enumerate` (so they can be in tables)

 * Several spacing fixes:
     - limit the width of `Pretty`-arranged monospaced code
     - cut out extra space characters in export lists
     - only escape spaces if there are _multiple_ spaces
     - allow type signatures to be multiline (even without docs)

 * Remove uninteresting and repetitive `main.tex`/`haddock.sty` files
   from `latex-test` test reference output.

Fixes #935, #929 (LaTeX docs for `text` build & compile)
Fixes #727, #930 (I think both are really about type families...)