Shortened codes status

[David Lucas]

This is a descriptive issue to keep track of progress on shortened codes' implementation. It lists all related issues and gives a glimpse on the key features.

• Issue #138 on generator matrix computation

Keypoints:

• encoder which computes generator matrix is available

• computes dimension without computing generator matrix

• keeps track of the original code

• one decoder available, which decodes using a decoder over the original code

• a test sheet for shortened codes is available in the experiments folder

See commit 7995b10 for the code and tests.