Font-lock haddock comments without whitespace

This allows haddock comments of the form

-- | Some
--
--Thing

where the second line doesn't have whitespace after the dashes. See
issue #201 for more information.
Font-lock haddock section headers
Determine yasnippet directory path in the correct load context

See #355
Switch haskell-process-cabal binding from "C-c c" to "C-c C-x"

"C-c c" is one of the bindings reserved for user-level customization,
as per https://www.gnu.org/software/emacs/manual/html_node/elisp/Major-Mode-Conventions.html.

Closes #317.
Fix guessing of cabal-process-type when set to 'auto

See #348
Introduce declarations to haskell-yas.el so it byte-compiles cleanly.
Merge pull request #344 from rootzlevel/haddock-font-lock

Haddock font lock
Don't redundantly mark haskell-font-lock-seen-haddock as local

It is already marked buffer-local where it is declared, so
make-local-variable is unnecessary.
More accurate regexes for haddock comments
Add hayoo backend for suggesting imports.
Hayoo should be the last resort for finding imports, due to speed
Just fetch hayoo results synchronously
Declare url-* vars to eliminate byte-code compilation warnings
Add "build --ghc-options=-fforce-recomp" to haskell-process-cabal choices
Add preliminary :loc-at based haskell-mode-goto-loc

@hvr We now have a number of ways to jump to things. I'll sit down and
consolidate these at some point. Technically all of them are different
and have different reliabilities, so doing a staged fallback of:

* :loc-at
* :i
* find-tag

Seems like a pretty robust way to almost always get something
useful. But for the time being before doing that I'll play around with
this and check for obvious bugs.
Show the type of the thing at point using :type-at

Think I'll also make this fallback on :t too.

@hvr
Nicely fontify types  from haskell-mode-type-at
find cabal sections referencing file

add completion options to cabal repl target selection
be smarter about selecting which section to add dependencies to