README.md: Fix indentation
README,md: Rewrite command descriptions

The goals of this change are:

  * to make the command descriptions as clear as possible
  * to make them agree terminologically
  * to make them agree stylistically
  * to bring them on the same level of detail
  * to sync them with code

All the descriptions were written from scratch. After that, they were
cross-checked with the code and the old descriptions to make sure
nothing important was missed.
Update patch for the "mail" module to match upstream
Merge pull request #391 from yast/update-mail-patch

Update patch for the "mail" module to match upstream
Stub MasterCFParser.pm

Stubbed because otherwise the "mail" YaST module will attempt to load
this file from the system, where it is broken.
Add bug number to the MasterCFParser.pm stub

Thanks to Martin Vidner for digging the bug.
Merge pull request #392 from yast/stub-master-cf-parser-pm

Stub MasterCFParser.pm
Merge pull request #390 from yast/readme-command-description-rewrite

[Review] Request from '' @ 'yast/ycp-killer/readme-command-description-rewrite'
Fix incorrect merge of README.md fixes

Pull request #390 was merged into master by mistake instead of #393
which obsoleted it (it mostly addressed review comments). This commit
attempts to fix that mistake and contains the diff between #390 and
Merge pull request #394 from yast/fix-bad-readme-merge

Fix incorrect merge of README.md fixes