Escape more special characters in regexps

In particular, start="\\\@<!\[" is the wrong way to define the start of
a region: it will work for \[, but also for \\[, which is erroneous.

if \\ and \[ are matched first, then you don't need to guard against a
preceding backslash.

Addresses https://github.com/guns/vim-clojure-static/issues/30
Remove unused clojureRegexpEscapes
Add tests for new regexp char escapes
Refactor \Q…\E region
Merge branch 'master' into development

* master:
  Refactor \Q…\E region
  Add tests for new regexp char escapes
  Remove unused clojureRegexpEscapes
  Escape more special characters in regexps
Remove leading backslash check from clojureRegexpBoundary

Unnecessary due to changes in master