tests runner and fixes concurrency option

Some minor changes to reflect correct exit codes related to command line option errors.

bug fix

There was a bug, when undefined steps followed after a failing step - suite was passing.

Multistep definitions and randomization of scenario execution order

2017-04-29

• added support for nested steps. From now on, it is possible to return
  godog.Steps instead of an error in the step definition func.
  This change introduced few minor changes in Formatter interface. Be
  sure to adapt the changes if you have custom formatters.

2017-04-27

• added an option to randomize scenario execution order, so we could
  ensure that scenarios do not depend on global state.
• godog was manually sorting feature files by name. Now it just runs them
  in given order, you may sort them anyway you like. For example godog $(find . -name '*.feature' | sort)

adds cucumber format

v0.6.3

fixes test case location matching and bumps version

fixes a bug

see #65

also fixes a bold color for matched argument, was lost while refactoring to colors package

print stack trace on panic

v0.6.1

use Options in FlagSet

event stream and run options

See changelog.md for more details

allow to run godog from outside the GOPATH

relates to #49

pretty printer fixes for outline examples

fixes #47

bug fix for background comment position

this released solved #43 and #44