ARROW-190: Python: Provide installable sdist builds

Author: Uwe L. Korn <uwelk@xhochy.com>

Closes #71 from xhochy/arrow-190 and squashes the following commits:

e28db45 [Uwe L. Korn] Add LICENSE and README to MANIFEST
f9943f5 [Uwe L. Korn] ARROW-190: Python: Provide standalone installable sdist builds

Author: xhochy

python/MANIFEST.in

@@ -0,0 +1,14 @@
+include README.md
+include LICENSE.txt
+
+global-include CMakeLists.txt
+graft cmake_modules
+recursive-include src/pyarrow *.cc *.h
+recursive-include pyarrow *.pxd
+
+global-exclude *.so
+global-exclude *.pyc
+global-exclude *~
+global-exclude \#*
+global-exclude .git*
+global-exclude .DS_Store