v1.3.4: Add option to disable completion in usage (#25)

* Add option to disable completion in usage

For some use-cases or operation systems, it might not be desirable to print usage information. That is why this commit introduces an option to disable completion information.
This addresses issue #20

* Detect completion support automatically

* Improve env handling

* Fix formatting

v1.3.3: Add padding to sub command list

Having large variations in the length of sub commands could lead to
inconsistent and ugly indention of the command synopses. This command fixes
this by calculating the longest command name beforehand and padding all command
names accordingly.

Fix error handling

v1.3.2

Fix error handling on exit-on-error

Rename to cmd

readme: Update according to go doc (#18)

* Update readme according to go doc

* Update readme according to go doc

Fix flag order and parsing

v1.2.0

Update readme according to go doc

Added positional arguments API

v1.1.0

Update readme according to go doc

First release

v1.0.0

Improve tests