Add entry point-style auto alias for "spacy"

Simplest way to run commands as spacy xxx instead of python -m spacy
xxx, while avoiding environment conflicts

MANIFEST.in

@@ -1,3 +1,4 @@
 recursive-include include *.h
 include LICENSE
 include README.rst
+include bin/spacy

bin/spacy

@@ -0,0 +1 @@
+python -m spacy "$@"

setup.py

@@ -187,6 +187,7 @@ def setup_package():
             url=about['__uri__'],
             license=about['__license__'],
             ext_modules=ext_modules,
+            scripts=['bin/spacy'],
             install_requires=[
                 'numpy>=1.7',
                 'murmurhash>=0.28,<0.29',