docs($injector): add example on how to use the element.injector

Closes #5188
chore(CHANGELOG): introduce perf() section for performance-related commits

Instead of using fix() or chore() when labelling a commit which improves
speed or performance use perf(). Perf commits will be listed in the
CHANGELOG under "Performance Improvements".

For example:
perf($animate): cache all getComputedStyle operations to reduce additional reflows
docs(guide/forms): clarify how NgModelController can be added to scope

Closes #5200
docs(tutorial): enlarge clickable area of tutorial nav buttons

Change position of <a> and <li> tags in tutorial nav buttons
partial. This allows the full area of the button to be clicked
rather than just the text.

Closes #5074
Closes #5209
docs(contribute) add platform agnostic git install link

Closes #5216
docs($q): correct typo in the 'Differences Q/$q' section

Closes #5230
docs($route): clarify examples of route parameters

Putting route parameter examples in braces was misleading newcomers.

Closes #5243
docs(input): remove redundant closing span tag

Closes #5257
style($route): make jshint happy

Fix the broken build and earn a late (french spelling).
docs(design): guide index formatting

Just my first pass at a more readable format of the guide index.

Note: the styles apply to all content in the docs, not just the guide
index. This is intentional and I feel that the result is positive.
docs(TRIAGING): Labels cla yes/no are automatically set

The labels are set by a script and
should not be set manually any more.
docs(TRIAGING): Add Type:Perf label
fix(input): prevent double $digest when using jQuery trigger.

If an event was performed natively, jQuery sets the isTrigger property.
When triggering event manually, the field is not present. Manually
triggered events are performed synchronously which causes the "$digest
already in progress" error.