Credstash

* New: stephen-164 added -f to `credstash get` for wildcard gets
* New: mrwacky42 added `credstash keys`
* New: evanstachowiak added `credstash putall`
* Updated: gene1wood, nkhoshini, and wyattwalter updated the docs
* Bugfix: pm990320 fixed a bug by adding pagination for large credential stores
* Bugfix: artburkart fixed a bug where writing csv files did not have proper line separators
* Removed: Python 3.2 removed from build matrix

* Set upper bound of `cryptography` to 2.1

* Only fetch the session resource and client once
* README updates for c and node imlpementations
* python 3.2 removed from build matrix
* fixed hmac checking
* removed build constraint on `cryptography` <2.0