Bump version to 0.7.0-SNAPSHOT
Rename 'artifactId' and change 'name'
Update JUnit dependency to 4.11
Rename two API methods

Version.lessThanOrEqualsTo()    => Version.lessThanOrEqualTo()
Version.greaterThanOrEqualsTo() => Version.greaterThanOrEqualTo()
Remove redundant conditional statements
Implement a Parser instead of RegExp

This commit also updates the code to comply with the SemVer 2.0.0.
Create MetadataVersion.NULL object, refactor
Create basic Expression types
Create Lexer for Expression parser

Factored out VersionParser.CharStream into a separate
class and made it generic to use in the Lexer. Did some
refactoring of VersionParser.
Create SemVer Expression parser
Add Javadoc to the source code
Prepare pom.xml for the repository
Update and reformat the README file
Add CHANGELOG file
Bump version to 0.7.0