Show usages of method does not find usages from md files

[vgheo]

work-around: Configure Find Usages > Search for text occurences

[idegtiarenko]

As mentioned in #17, plugin only provides ognl expression parsing and linking to concordion files. For that it relies on "Inject language" feature that is available for some of the AST tree nodes.

Unfortunately existing MD plugins does not allow this, so it was required to use hackysolution called org.concordion.plugin.idea.injection.ConcordionInjection. The same way, this issue could be closed by providing new plugin to parse MD that also allows to do LanguageInjection in places where concordion expression could be.