Add a .gitattributes file.

This ensures all text files are properly marked as such from git's
perspective. This will allow it to determine whether it should convert
line endings to the platform's native endings on checkout, for a given
file.

The Python-specific parts were sourced from here
https://github.com/alexkaratarakis/gitattributes/blob/master/Python.gitattributes
For all other files, it lets git's heuristics determine whether it is
a text file.

.gitattributes

@@ -0,0 +1,28 @@
+# Set the default behavior, which is to have git automatically determine
+# whether a file is a text or binary, unless otherwise specified.
+
+* text=auto
+
+# Basic .gitattributes for a python repo.
+
+# Source files
+# ============
+*.pxd       text diff=python
+*.py        text diff=python
+*.py3       text diff=python
+*.pyw       text diff=python
+*.pyx       text diff=python
+
+# Binary files
+# ============
+*.db        binary
+*.p         binary
+*.pkl       binary
+*.pyc       binary
+*.pyd       binary
+*.pyo       binary
+
+# Note: .db, .p, and .pkl files are associated
+# with the python modules ``pickle``, ``dbm.*``,
+# ``shelve``, ``marshal``, ``anydbm``, & ``bsddb``
+# (among others).