Tweak install options and update installation instructions in readme

Author: almarklein

README.md

@@ -31,7 +31,8 @@ Uvicorn currently supports HTTP/1.1 and WebSockets. Support for HTTP/2 is planne
 Install using `pip`:
 
 ```shell
-$ pip install uvicorn
+$ pip install uvicorn[pure]  # Install pure Python deps (works anywhere)
+$ pip install uvicorn[fast]  # Install fast deps (not for e.g. Windows or Pypy)
 ```
 
 Create an application, in `example.py`:

requirements.txt

@@ -1,4 +1,6 @@
 click
+
+# Pure
 h11
 
 # Optional

setup.py

@@ -3,7 +3,6 @@
 
 import os
 import re
-import sys
 
 from setuptools import setup
 
@@ -60,17 +59,10 @@ def get_packages(package):
     author_email='[email protected]',
     packages=get_packages('uvicorn'),
     data_files = [("", ["LICENSE.md"])],
-    install_requires=[
-        'click'
-        'h11',
-        'wsproto'
-    ],
+    install_requires=['click'],
     extras_require={
-        'full': [
-            'uvloop',
-            'httptools',
-            'websockets>=6.0'
-        ]
+        'pure': ['h11', 'wsproto==0.13.*'],
+        'fast': ['uvloop', 'httptools', 'websockets>=6.0'],
     },
     classifiers=[
         'Development Status :: 4 - Beta',