Fixes for DV

[kudanai]

I've made some updates to the DV specifications. I think with these additions the phonemiser output is sensible enough for now. Some of the rules are obviously simplified since their actual rules are more complex and probably require fst

The following changes were made:

• Add missing char ޱ in alphabet.txt
• Fix phons.tsv
  • Add rules for pre-nasalised consonants
  • Make އް and ށް default to stops. This is a sensible default for them. Should sound fine 90% of the time
  • default ން to voiced retroflex nasal.
  • fix vowel rules that were previously tied to consonant އ, preventing proper placement
  • Other minor adjustments to consonant maps

[ftyers]

Looks good, can you update the alphabet code to remove the newlines though? (otherwise it might try and add newline as a symbol).