tag: small changes

* rewrite initialize()
  * to use class method
* remove is_tag_line()
  * to be is_snip_tag_line() / is_snippet_tag_line()
spec/test: use byebug and debugger to debug

* use byebug
* use debugger (ruby version < 2.0.0)
tag: add is_snip_tag_line() / is_snippet_tag_line()

* to find @snip/@snippet tag
tag: add is_snip_or_snippet_tag_line()
tag: add is_tag_line_with_repository()
tag: add get_repo()
tag: add get_path()
tag: add get_prefix()
tag: add get_suffix()
tag: add get_spaces()
tag_parser: add find_snip_tags()
tag_parser: add find_snippet_tags()
tag: add to_snip_tag() / to_snippet_tag()
Merge branch 'wip/tag-parser/1408338260' into feature/insert-snippet

* tag_parser: add find_snip_tags()
* tag_parser: add find_snippet_tags()