Simplified bitsize calculation

[adamantike]

Binary representation through format string syntax. It also checks earlier if parameter is an integer, so it fails for num = 0.0 instead of returning 0 (current behaviour).

[coveralls]

Coverage increased (+0.02%) to 90.877% when pulling f1aedea on adamantike:simplified-bit-size into a548782 on sybrenstuvel:master.

[coveralls]

Coverage increased (+0.3%) to 91.111% when pulling a8a8f94 on adamantike:simplified-bit-size into a548782 on sybrenstuvel:master.

[sybrenstuvel]

This is a good target for refactoring indeed. Now that we no longer have to support Python 2.6, we can simply use int.bit_length() instead. I implemented this in 5e08c91.