added versioneer for versioning

The versioneer code is kept in _version.py so that version.py can
be left alone for backwards compatibility

Author: alorenzo175

.gitattributes

@@ -0,0 +1 @@
+pvlib/version.py export-subst

MANIFEST.in

@@ -1,6 +1,8 @@
 #include *.txt
+include versioneer.py
+include pvlib/_version.py
 recursive-include pvlib/data *
 include README.md
 include pvlib/spa_c_files/*.h
 
-#recursive-include docs *.txt
+#recursive-include docs *.txt

pvlib/__init__.py

@@ -11,4 +11,4 @@
 from pvlib import tracking
 from pvlib import pvsystem
 from pvlib import spa
-from pvlib import modelchain
+from pvlib import modelchain