v3
initial support for jinja2-like macro import functions
extends template set to track all macro names for "from" condition, instead of only matching those macros where "export" is provided
"from" keyword on macro import, ignores but consumes "with context"
results in syntax support for
-- {% from "macrofile.extension" import name_of_macro with context %}
Adding slice/array-support for Value.Contains().
Fixes #71
Merge remote-tracking branch 'origin/v3'