[yaml-plus mode] Enhance YAML mode

Pure YAML does not seem to have the possiblity to re-use definitions;
this mode highlights any definition re-use like `${definition}`.
Merged `yaml-plus` mode into `yaml`
Removed ugly /re/ hint
[rst] Emphasis and literal highlighting fix

Ensured that emphasis (weak & strong) plus literal syntax highlighting are rendered correctly even if the highlighted word is followed immediately by a non-word character (like an interpunction):

 * ```a word **strongly emphasised**?```;
 * ```a word *weakly emphasised*?```;
 * ```a word with ``literal emphasis``?```;

Further changed recognition order to `strong`, `weak`, `literal`, `number`, `positive`, `negative` and `link` to comply more with the reStructuredText spec (see http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html#recognition-order).
[rst] Reference name fix w.r.t. "phrase-references"

Phrase-references should be able to contain interpunction characters; fixed.
[smalltalk mode] add support for "#'...'" symbol syntax
[tern addon] Fix a few bugs
[tern addon] Pass file name and document to fileFilter
Add -moz-box-sizing rules to the styles that use box-sizing

Apparenly Firefox still hasn't caught up on the unprefixed version.
Propagate StringStream's match() fixes to runmode
[vim keymap] Define a vim option, register beforeSelectionChange handler

Issue #1084
Issue #1630
Fix bug in findWordAt

Which could result in a selection at a negative character offset
when double-clicking.

Issue #1638
[real-world uses] Add Fiddle Salad
[compression helper] Sort and complete addon scripts
[merge addon] Make sure synchronized scrolling scrolls other pane to top/bot
[merge addon] Synchronize vertical scrolling
[merge addon] Use CodeMirror-merge-* CSS class names

Since the addon is called merge, not diff.