DyNet 2.0.1

DyNet v2.0.1 made the following major improvements:

Simplified training interface: #695
Support for multi-device computation (thanks @xunzhang !): #704
A memory efficient version of LSTMBuilder (thanks @msperber): #729
Scratch memory for better memory efficiency (thanks @zhisbug @Abasyoni !): #692
Work towards pre-compiled pip files (thanks @danielhers !)