Raise Liquid::ArugmentError when condition has wrong usage

Condition now raises ::ArgumentError when built wrongly.
This patch make it raise Liquid::ArgumentError instead
to indicate a liquid markup error instead of ruby error.
remove template return
Merge pull request #347 from Dillon-Benson/patch-1

remove template return
Move date coercion to `#to_date`
Merge pull request #351 from Shopify/date-cleanup

Move date coercion to #to_date
render! will properly force rethrow of errors if context is passed as an argument
Merge pull request #349 from Shopify/render_bang_allow_not_safe_contexts

render! will properly force rethrow of errors if context is passed as an argument
use attr_writer instead of error_mode= method
Merge pull request #354 from Dillon-Benson/patch-3

use attr_writer instead of error_mode= method
add test for numerical sort
Add error messages for missing variables when :strict
Merge pull request #352 from gaiottino/master

Add error messages for missing variables when :strict

Conflicts:
	History.md
Update docs badge in README

Update the URL of the docs badge to include it from inch-ci.org instead of inch-pages.github.io (the former being the successor of the Inch Pages project).

[ci skip]
Merge pull request #363 from rrrene/patch-2

Update docs badge in README
[Liquid] Add round, ceil and floor standard filters
Merge pull request #368 from Shopify/add-round-ceil-and-floor

[Liquid] Add round, ceil and floor standard filters
add additional tests for https://github.com/jekyll/jekyll/pull/2505
Unfreeze version string

It breaks gem installation on ruby 1.9.x (older rubygem?)
Merge pull request #371 from Shopify/unfreeze-version-string

Unfreeze version string
Canonicalize travis ruby versions