[#24,bugfix][s]: fix breakage to install cmd caused by upgrade to latest datapackage-read.

* spec parsing now in datapackage-spec and not datapackage-read but had not changed dpm code
* Bad: had not run test before release :-(
[doc][s]: remove obsolete doc for removed commands.
[doc][m]: all command docs in the doc/command-X.md files.

* Also add doc for help command which we use to provide usage
* Also remove docs from README so we do not get out of sync