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.
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
Do not intall stackprof under jruby nor rubinius
rbx-19mode is not supported anymore
Fixed relative link
Merge pull request #375 from Shopify/relative-link

Fixed relative link
Merge pull request #374 from Shopify/remove-duplicate-ruby-version

Give some :heart: to travis.yml
Allow tag classes to be reloaded when using Liquid.cache_classes is false

Because Liquid keeps a reference to tag classes, Rails class reloading may
cause problems with custom tags. This commit introduces a setting that
allows these classes to be resolved when required.
Merge pull request #376 from Shopify/tag-class-reloading

Avoid holding on to stale tag classes
add regression tests for #377
Revert "Merge pull request #352 from gaiottino/master"

This reverts commit 553b0926ae28103475fd66e6637af855a81ddb0e, reversing
changes made to 628ab3dc6a702d87340a6fdd9715d9ef54fab786.
Merge pull request #378 from Shopify/revert_352

Revert: Add error messages for missing variables when :strict
Optimize checking for interrupts by replacing any? with NOT empty?