Fixed documentation URL
Split impl.dart into client and server parts to be able to selectively include the one you need

fixes #41
Adapt tests to impl.dart split

fixes #41
Adapt command line utility to impl.dart split

fixes #41
Updated README so that bullets are correctly shown in pub
Removed unused imports
Updated README so that bullets are correctly shown in pub
Change in doc
Implementation of OFB mode of operation
Implementation of CFB mode of operation
Implementation of ECB
Corrected typo
Removed unused variable from tests
Let NullBlockCipher use arbitrary block sizes
GCTR implementation and refactor of modes of operation factories, which were wrong
Prepare version release: 0.5.1
Merge branch 'fixes' into development
Point to next version: 0.6.0