ragel implementation of BEL parser

provides observable parser that allows for different user actions for
the same Parser.parse call

downsides:
  - existing parsing bug requiring new lines between some BEL statements
  - cannot parse document comments correctly
  - nested BEL statement groups are not supported
  - Parser.parse requires all contents to be read in to memory

refs #2
removed dependency on antlr gem

refs #2
bumped version; minor update due to ragel parser
pop statement stack to reach the first statement
handle block passed to Parser.parse

updated specs to pass; added observer spec for Parser.parse method

show documentation format when running rspec (Rakefile)
bel syntax for Parameter/Term/Statement using to_s

added rspec test
fixed statement group annotation issue; rels as symbols
strip leading and trailing quotes in parameters
read annotation name on UNSET
support parsing of DEFINE for belns/belanno urls
all parsed provide to_s; allows serialization

fixed parsing of STATEMENT_GROUP
progress on parser completion

fixed doc comment

fixing term function parsing;
fix conversion of annotation list to BEL syntax
non-identifier matcher now excludes _

bug with Parameter BEL syntax not properly quoting value
fixed namespace definition BEL syntax
notify of parsed parameters
updated BEL parse example in README
factor LIST syntax to common.rl
refactor keywords and basic actions into common.rl
supporting LIST and PATTERN annotations