ctx31 rmsubstr: now removes reverse complements

ctx_rmsubstr.c:
- remove substrings even in reverse complement
- added -F,--format option to specify output format
- added -v,--invert option to print only substring entries

dna.c:
- dna_revncasecmp() compare sequence `a` against reverse complement `b`

seqout.h:
- seqout_gzprint_read() and seqout_print_read() for printing reads in given format