Fix typo in a file name.

renamed:    enginioqmloblejctadaptor_p.h -> enginioqmlobjectadaptor_p.h
Add comment about a bug.
Fix invalid overloading in EnginioQmlClient

C++ says that inheritance, by default, hides a function member, to make
it properly overloaded "using" key word has to be used.
Merge pull request #47 from nierob/smallFixups

Small fixups