Fix for doc reference to python "raise" statement
Fix for doc reference to python "raise" statement

:ref:`py:raise` -> :ref:`raise statement <py:raise>`

Before fix the text reads: "...define an on_error handler consisting
of a single empty The raise statement."　After fix it should read: 
"...define an on_error handler consisting of a single empty raise
statement."
Harmon758/discord.py,Rapptz/discord.py,Harmon758/discord.py,rapptz/discord.py