enable travis ci support
add travis-ci badge to readme.md

visualise travis state
use default task as test task for 'npm test' script

this seems more simple
update dependencies to latest versions
cleanup output of exception

the item indeed is a po item and has references. The old behaviour was
tailored to an older implementation of the fix.

Conflicts:
	lib/extract.js
fix the duplicate msgid detection fix

there has been an edge case, that has been taken care of, now.

Conflicts:
	lib/extract.js
split out history into ChangeLog.md file

ChangeLog might grow quite large, so better keep it separate from the
README

Conflicts:
	README.md
allow empty po files (no strings defined)

show a warning, to inform about this.
fix problem with trailing white-space in translated strings

trailing white-space have been removed, before. This is wrong, since
extracted strings should not be changed in any way.
Release v0.5.1