Even if key_column is not 'id', the route_param is.
Ensure the id param is the one from the route.

Just in case the user has a column named 'id' too, that would be in the body
params - if we say `params('route')` we can be confident we get the right one.
Get params from body only.

For safety, in case the uer has a column named 'id' which isn't the primary key
- where the id in the route would conflict.

Cheers to tobyink on IRC.
Merge pull request #40 from bigpresh/fix_key_column

Even if key_column is not 'id', the route_param is.