added liftover module, used for dyncamically converting coordinates between coord systems
added dseg cython extension
added ability to write to uint8 wiggle with file descriptor
allow wiggle values to be written to gzf or fd
corrected bug in error message
corrected bug introduced by last trackstat commit
added function to test whether file is gzipped by reading first two bytes
modified several scripts so they no longer default to hg18 assembly
added option to report chromosome ids