r55: merge PE fasta/qr55: merge PE fasta/qr55: merge PE fasta/qr55: merge PE fasta/qr55: merge PE fasta/q
r56: drop SE from interleaved PE fasta/q
r57: segfault when reading from stdin
trimming adapters
debugging to stderr!!!
change the way stdin is read

When a program is submitted via bsub etc., isatty(fileno(stdin))
is always false. The old seqtk will attempt to read from stdin
which is empty. This commit ignores stdin if a file is provided.
bugfix: %0 may happen
bugfix: another %0 bug
r63: a bug caused by the previous fix
r64: mask by max qual
Output the comment if there is one in trimadap.c
opt to remove adaptor sequence from read sequence

This implements a CLI flag to actually remove the adapter sequence from
the read's sequence, instead of just masking it out. The quality string
is correctly removed also.
r65: cutN supports fastq output
r66: compute frequency of a kmer+neighbor
r67: 2-pass sampling for low RAM
Merge remote-tracking branch 'upstream/master'

Conflicts:
	seqtk.c
Merge commit '007486e'
Merge commit '371d48c'