Default pe_period to None

When using original or no Positional Encoding, pe_period should not have a default value. When using regular PE, the pe_period parameter must now be explicitly given.

Attention window

Add an attention window, as a rectangular window on the attention scores. The aim is to help the network focus on local patterns, without affecting the attention scores themselves.

Time length independance

This new version restructure the package (file renaming, extra feature removing) and makes Transformer able to compute on arbitrary long time sequences.

Initial release

v0.1.0

Add package install scripts