Using samtools tview as a library

See my blog for more information : http://plindenbaum.blogspot.fr/2013/01/samtools-tview-as-library-to-display-bam.html

added some callbacks to tview_t  and removed everything related to ncurses. Created some 'conrete' instances of this structure to display the bams with ncurses, html and tty.

![jeter](https://f.cloud.github.com/assets/33838/97841/04b8b0f6-670a-11e2-8b54-6ee683d39b7c.jpg)