Tidy requirements by removing transitives (#120)

* remove cffi and cryptography
* remove openssl transitive requirements
* remove remaining transitive requirements
* alphasort requirements
* remove ssl dev notes from readme

README.md

@@ -13,17 +13,6 @@ A reference client library for the Open Library API. Tested with Python 2.7, 3.5
 
 ## Installation
 
-As a prerequisite, openlibrary-client requires libssl-dev for the cryptography used in openssl. for Ubuntu kindly use the following command:
-
-```
-$ sudo apt install libssl-dev
-```
-
-For Fedora/RHEL, use the following command to install libssl-dev for crypptography used in openssl.
-```
-$ sudo dnf install openssl-dev
-```
-
 If you plan on doing MARC parsing, you'll need `yaz` (see: https://github.com/indexdata/yaz). Assuming Ubuntu/debian, you can install `yaz` via apt:
 
 ```

requirements.txt

@@ -1,16 +1,7 @@
 backoff==1.3.1
-cffi==1.8.2
-cryptography==2.3.1
-enum34==1.1.6
-idna==2.1
-ipaddress==1.0.16
-ndg-httpsclient==0.4.2
-pyasn1==0.1.9
-pycparser==2.14
+internetarchive==1.8.1
+jsonpickle==0.9.3
+jsonschema==2.6.0
 pymarc==3.1.5
-pyopenssl==17.5.0
 requests==2.20.0
 six==1.10.0
-jsonpickle==0.9.3
-jsonschema==2.6.0
-internetarchive==1.8.1