Add 'the easy way' basic instructions to README file
Create a MyMoip::Purchase class to provide an easy way to checkout

Unfinished but working class. Using Minitest/Spec style for tests.
Rename MyMoip::Purchase#credit_card_owner to #payer

Equal to MyMoip's class name.
Remove jeweler dependency for gem generation
Merge remote-tracking branch 'origin/master' into purchase-class

Conflicts:
	README.md
Convert Purchase's tests to minitest's unit syntax
Rename required keys in README example of Purchase use
Merge branch 'remove_jeweler' into purchase-class

Conflicts:
	mymoip.gemspec
	test/helper.rb
Remove explicitly minitest requirement
Improve identation and (single) quotes use in README
Merge branch 'purchase-class'