Make tests actual integration tests
Merge pull request #416 from Shopify/filter-quirks

Make Filter Quirks Tests Actual Integration Tests
Profile liquid rendering

Add a simple profiling system to liquid rendering. Each
liquid tag ({{ }} and {% %}) is processed through this profiling,
keeping track of the partial name (in the case of {% include %}), line
number, and the time it took to render the tag. In the case of {%
include %}, the profiler keeps track of the name of the partial and
properly links back tag rendering to the partial and line number for
easy lookup and dive down. With this, it's now possible to track down
exactly how long each tag takes to render.

These hooks get installed and uninstalled on an as-need basis so by
default there is no impact on the overall liquid execution speed.
Call to_liquid in Context invoke
Merge pull request #414 from Shopify/to_liquid_context

Call to_liquid in Context invoke
Simplify filter parse regex
Simplify secondary filter regex
Merge pull request #417 from Shopify/simplify-regex

Simplify Variable Parsing Regexes
Merge pull request #364 from collectiveidea/instrument-rendering-with-hooks

Profiling the rendering of a liquid template
Implement the stack based interpreter from the leg_c branch.
Flatten array of expression instructions to reduce object allocations.