BEAST v2.6.6 release

Fix so that when not using ambiguities, the nucleotide 'U' base pair is correctly interpreted
Fix tree annotator for lower bound on common ancestor heights
Make the -prefix option work when not using a directory
Allow '=' signs in options passsed with -D
Add filter input to SwapOperator
Fix so DocMaker works again
Update for R script to create EBSP plots
Limit size of Trie to prevent memory leaks for some models
More robust Nexus parser
Improved error messages