TACHYON-103 Remove public modifiers in method defined in interface.

Change Javadoc from @code to @link for TachyonFSCore in AbstractTachyonFS.

TACHYON-103 Update doc about style to define method in Java interface.
Merge pull request #413 from hsaputra/remove_public_interfacemethods

TACHYON-103 Remove public modifiers in method defined in interface.