README.rest synced with man page, reality
osc(1) abstracted away from "main"...

... to bring it to the level of abstraction of the rest of it.
-b causes osc build just before osc ci
-C causes skipping of osc ci
-d . uses git archive

getting closer to comfortable bs-update-centered workflow:

  > git clone ... mypackage
  > cd mypackage
  > edit
  > git ci
  > bs-update -Cbd . HEAD x.y.z

if all went well, one could go on with

  > git tag -a vx.y.z
  > bs-update vx.y.z

the major missing piece ATM is the "x.y.z" argument above in

  > bs-update -Cbd . HEAD x.y.z

(it would set $bsu_version); we have bsu_version_hook() but
that is suboptimal for this use-case: it's too much work to
put in place compared to adding an argument, and needs to be
disabled again before dropping -C.
usage mentions two operands (<tag> [<version>])
bs-update's second argument sets $bsu_version

$bsu_version is set using the first good of these sources:

* $2
* bsu_version_hook
* $bsu_tag
bs-update <tag> <version> tested
rpmlint complains about trailing dot in Summary
rpmlint complains about nonstandard package group
manpage: FILES/Variables updated

* bsu_version cannot be set in config files
* bsu_bs_commit, bsu_dryrun, bsu_test_build documented
manpage revamp

* option descriptions do not mention config variables;
  it was awkward
* bsu_version is internal, no mentions
manpage: example is more realistic now
manpage: FILES/Variables section takes less space
README.rest and manpage synced again