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