Add tests for text merging

failures (36):
    de::tests::merge_text::cdata_and_cdata
    de::tests::merge_text::cdata_and_text
    de::tests::merge_text::comment_between::cdata
    de::tests::merge_text::comment_between::cdata_and_cdata
    de::tests::merge_text::comment_between::cdata_and_text
    de::tests::merge_text::comment_between::empty_cdata_and_text
    de::tests::merge_text::comment_between::text
    de::tests::merge_text::comment_between::text_and_cdata
    de::tests::merge_text::comment_between::text_and_empty_cdata
    de::tests::merge_text::empty_cdata_and_text
    de::tests::merge_text::pi_between::cdata
    de::tests::merge_text::pi_between::cdata_and_cdata
    de::tests::merge_text::pi_between::cdata_and_text
    de::tests::merge_text::pi_between::empty_cdata_and_text
    de::tests::merge_text::pi_between::text
    de::tests::merge_text::pi_between::text_and_cdata
    de::tests::merge_text::pi_between::text_and_empty_cdata
    de::tests::merge_text::text_and_cdata
    de::tests::merge_text::text_and_empty_cdata
    de::tests::triples::cdata::cdata::cdata
    de::tests::triples::cdata::cdata::end
    de::tests::triples::cdata::cdata::eof
    de::tests::triples::cdata::cdata::start
    de::tests::triples::cdata::cdata::text
    de::tests::triples::cdata::text::cdata
    de::tests::triples::cdata::text::end
    de::tests::triples::cdata::text::eof
    de::tests::triples::cdata::text::start
    de::tests::triples::start::cdata::cdata
    de::tests::triples::start::cdata::text
    de::tests::triples::start::text::cdata
    de::tests::triples::text::cdata::cdata
    de::tests::triples::text::cdata::end
    de::tests::triples::text::cdata::eof
    de::tests::triples::text::cdata::start
    de::tests::triples::text::cdata::text

Author: Mingun