added writeHeaderFile() method to PrefixUnionDict, and ability to construct PrefixUnionDict directly from header file.
added writeHeaderFile() method to PrefixUnionDict, and ability
to construct PrefixUnionDict directly from header file.

RitwikGupta/pygr,ctb/pygr,ctb/pygr,cjlee112/pygr,theoryno3/pygr,GenDataPro/pygr,ctb/pygr,cjlee112/pygr,cjlee112/pygr,cjlee112/pygr,GenDataPro/pygr,RitwikGupta/pygr,ctb/pygr,ctb/pygr,RitwikGupta/pygr,theoryno3/pygr,theoryno3/pygr,GenDataPro/pygr