added usage example for ResourceIndex
fix setting rel object using RDF uri
rework BEL::Script parser API for usability

remove Observer pattern usage

can now parse by passing a block or using the return value as Enumerable

1. block
BEL::Script.parse('p(HGNC:AKT1)', {HGNC: HGNC}) do |obj|
  # handle obj
end

2. enumerable (each)
BEL::Script.parse('p(HGNC:AKT1)').find_all {|x| x.is_a? Parameter}.to_a

updated API examples in README
updates tests
updated bin scripts
updated ragel parser to yield parsed objects