plot-bamstats: better support for plots of single-read bams
stats: Accept string flags with -f/F
plot-bamstats: Generate summary html page
plot-bamstats: Use 0x1 rather than 0x2 flag to detect paired-end

sequencing. Prevent divison by zero with all reads unmapped.
plot-bamstats: fixes in create_html and gz input
Man page minor edit and whitespace canonicalisation
Merge bug fixes for #183 and #262

Also add summary HTML index page.
Use "%s+htslib-%s" version format