documentation update

Adjust/relocate the BCF1 and calling text as desired.

* clarify `--phased` option in `bcftools view`. Fixes (#92)
* add some man text about BCF1
* add some man text about calling no with `call` rather than `view`
* add in man doc for recent changes to `bcftools index`
Merge pull request #94 from mcshane/feature/docs

documentation update