add an interface to represent the atomic elements of source code
add some methods to IAtomicElement
add a template of Token
add an enum to describe types of elements
add a class to map source file and its contents
add an interface to describe how to parse each source file
[MINOR_CHANGE] correct wrong spelling
implement Token
add a class to represent segments
add a class to have contents of segments
override equals, hashCode, and toString in Segment
[MINOR_CHANGE] fix wrong comment
implement equals, hashCode, and toString of Token
[MINOR_CHANGE] fix wrong comment
implement equals, hashCode, and toString of SegmentContent
implement equals, hashCode, and toString of SourceFileContent
update comments