Ruthlessly tidied up the examples directory.

The Makefile and C programs are gone. They didn't build and mostly
were redundant anyway. Arguably chk_indel.c and bam2bed.c could still
have a use, but as toy examples they would belong in an htslib rather
than here anyway.

The README file was updated to use more modern command alternatives
(view vs import, mpileup vs pileup), but does not yet contain any
references to CRAM.  This can be added once -T is working.