consolidate parse api to BEL::Script.parse method

added spec tests for parsing from file-like object

updated README with iterative parse example

refs #8
added to_s / to_sym to Function
map resource Keyword to ruby symbol
remove unused require stmt
generalize loading published resource indices

added ResourceIndex.openbel_published_index(version) method

updated integration spec
updated README example
lazy enum for parser if available ( >= ruby 2.0 )

refs #8
ref "latest-release" namespaces
bumped rake gem version to 10.3
removed superfluous module includes
clean up BEL parser; can now run script.rb as main
corrected parse example
move rubinius to rbx-2; should fix travis build
missing require needed for Dir::tmpdir
allow read/write variables on BEL::Language::Term