[merge addon] Add highlightDifferences option and method

Provides new option (highlightDifferences) and method highlightDifferences(bool)
to the MergeView plugin.

If true (or undefined) the original behaviour is maintained, which is to show
the differences (line highlighting and gutter graphics), if false then
the changes will not be shown.

Calling the method causes the visual change to occur 'immediately'

Signed-off-by: ciaranj <ciaranj@gmail.com>
[merge addon] Clean up showDifferences option

Issue #1765
Add "gutterContextMenu" event to capture context menu events in gutters
Clean up gutterContextMenu code

Issue #1766
[project page] Set border: 0 for logo

Woah, IE still defaults to a border around images in links.
Fix bug introduced by previous contextmenuInGutter patch

Issue #1766
Use zero-width space in context-menu select-all hack

To prevent the mouse click from landing outside of the selected
text, which broke copy in IE.

Closes #1764
[project page] Add links to a few more demos
Fix problem in workaround for Webkit's failure to render huge text nodes
Experimental option crudeMeasuringFrom

Stopgap for #1022
Remove outdated note from LICENSE

Subdirectories no longer contain separate LICENSE files. Delete
the note to them from the top level LICENSE.
Remove redundant line in AUTHORS

Removed the redundant "List of contributors..." line
[merge addon] Shows differences when the non-edit pane is updated

Previous behaviour was to only update the displayed differences if
the edit pane was modified.  There exists use-cases such that the
differences should be updated when any of the panes change.

I don't expect this to introduce any performance regressions due
to the existing debounce code within the update function.

Signed-off-by: ciaranj <ciaranj@gmail.com>
Allow linter to run on windows

Node provides some cross-platform utility methods to enable safe
path traversal.

This change merely swaps out a hardcoded '/' (unix path separator)
to use one of these methods.

An alternative strategy would be to use the constant 'path.sep' but
this felt 'cleaner'.

Signed-off-by: ciaranj <ciaranj@gmail.com>
Main CSS file: Clean-up and fix lint warnings

Use 0 instead of 0px, clean-up two line breaks, to fix lint warning;
Three empty CSS blocks could also be removed.
[fullscreen addon] Reduce z-index in order to not hide completion popups
[scss] Fix indentation issues

Closes #1776
[css mode] Fix unused variable
[coffeescript mode] Stop highlighting .keyword (.on/.off/.in) as error

Closes #1779
[matchtags addon] option added to highlight both tags