Split test_quotefordtd() and add more asserts to resulting functions

test_quotefordtd() hosted asserts both for quotefordtd() and
unquotefromdtd(), and thus it must be splitted.

Added more asserts for the last escaped characters conversions included.
Changed tests for support testing percent sign escaping

Changes test_quotefordtd() and test_unquotefromdtd() in order to add
tests for future percent sign escaping tests
Add support for % character escaping and unescaping
Add comment to test_escapes() explaining why is overwritten
Change Android DTD method names to match DTD method names

This will ease future refactors in these tests.