Fix cross-iframe issue with length filter

The length filter's instanceof checks were producing erroneous output when
handling data originating from another iframe. This commit fixes the issue by
replacing those instanceof checks with usage of Twig.lib.is checks.
fix windows filesystem relative path
fix windows path relative
Fix to macros. The way it was written, passing arguments of false or 0 become undefined.
Forgot to run make.
Small fix to macros.
Implemented batch filter
add dist files for travis
Implement round filter
Merge PR #157 and rebuild
Merge PR #159
Merge PR #161 and rebuild
Merge PR #162 and rebuild
Bump version to 0.7.2 and rebuild
Merge branch 'master' into fixtures-tests-iterable