Fixes for TLSA impl., TXT, and fixtures. Combines PRs #2 and #3 from @rakoo

Fixed bugs in TLSA and TXT support. Improved fixtures testing.

+ Fixed implementation of TLSA (hopefully)
+ TLSA value is now stored as a raw byte Buffer in the 'buff' field
+ TXT records support an array of texts. 'data' is now an array.
+ TXT records now support UTF8 (since RFC says to treat as binary info)
+ Added TODOs to comments
+ Noted buggy support for SRV records
+ Updated fixture for TLSA record
+ Fixed fixture for TXT record