Added has_tag helper to coreHelpers, added has_tag unit tests. passing OK
Merge pull request #1539 from niedbalski/master

[Feature Request] Theme API: add has_tag helper to coreHelpers.
Modified ghostdown markdown extension to allow for 4+ inline underscores

See #1113
- added additional regex rule to replace 4+ underscores with their coded equivalent: &#95;
add test for allowing 4 underscores in markdown
Merge branch 'markdown-underscores' of https://github.com/bastilian/Ghost into markdown-underscores