wrote documentation for user module
adjusted ignore-list
added test module

* added module for testing modules which use the database module
* adjusted the user module test
improved database test module

* moved setting of datadir to separate subroutine so it can be
  called/reset several times during the test
* added POD regarding the author and licence
added test utility module
adjusted database test by using test modules
added version number
improved description
replaced base pragma with light-weightier parent pragma
added stock module

* added initial implementation
* wrote documentation
* added appropriate tests
added price/bottle calculation and test