Rakefile: support rspec 3.1
git: ignore vendor dir
git: ignore .pryrc
gem: use pry and pry-byebug
gem: use version_sorter
social_snippet: add SnippetFinder classes
social_snippet: add RepositoryManager class
social_snippet: add Inserter class
social_snippet: add Snippet class
context: support repository's reference
config: make private internal methods
version: move methods from repository
version: test: add tests from repository_test
repository: support version refs
repository: add test for version features
tag: support references
tag: spec: add tests using reference
tag_parser: change instance methods to class methods
tag_parser: spec/test: change instance methods to class methods
social_snippet: use external classes