Add dcumentation (#12)

* added sphinx documentation
* filled in most missing docstrings
* updated README and setup.py, added CONTRIBUTING
* added docs build target

.editorconfig

@@ -0,0 +1,27 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+charset = utf-8
+
+[*.py]
+indent_style = space
+indent_size = 4
+
+[*.rst]
+indent_style = space
+indent_size = 3
+
+[{package.json,package-lock.json}]
+indent_style = space
+indent_size = 2
+
+[*.{yml,yaml}]
+indent_style = space
+indent_size = 2
+
+[Makefile]
+indent_style = tab
+