Unit tests for block comment, line comment on empty lines, line comment
auto-switching to block comment & vice versa, and commenting in mixed
syntax modes.

The commented-out tests don't pass yet.
Update block-comment unit tests to account for pull reqs #2121 (handle line
comments differently), #2133 (single-line block comment mode when Line
Comment invoked in CSS/HTML/etc. - enable test coverage), and #2148 (don't
replace whole selection - which means tests must work around #2335).
Add more tests & change expected behaviors per #2337 and pull #2342.
Clarify comments now that code's expected behavior follows simpler rules.
More block-comment unit tests: cases where selection extends outside bounds
of multi-line comments (per NJ); cases where selection edges are in
whitespace (tricky cases in current implementation since token info is
ambiguous); case with two immediately adjacent block comments.
Adds sass support

This commit requires that codemirror be updated to include sass first.
I have already submitted this change
Add support for opening files at startup.
Fix bug #2813 (Go to Definition can't find toString() methods) - Use
hasOwnProperty() with StringMatcher caches instead of simple truty checks
that will see Object.prototype members too.
Add unit tests for StringMatcher & JSUtils to cover this (JSUtils already
works, but that might have just been luck; it's equally as susceptible).

Plus a few docs clarifications in code I ran across while doing a quick
skim for other instances of this bug.
Fix another case of #2813 - Quick Edit for JS crashes if invoked on a
toString() call.

Add a unit test for this case too, doing some sizable cleanup to the
findMatchingFunctions() test suite in the process - removed unused code,
centralized duplicated setup/harness code.
Update Getting started screenshot for 'de' locale, transparent background
Translated strings for sprint 20
Use master branch on build status badge
There is no need to extend the replaced text when adding a :
Disable two unit tests due to marijnh/CodeMirror#1255. Bug already filed
to track re-enabling them.