Revised Compression Method

[lafncow]

I made 2 changes to the "compress" method:

1. it will return fewer than the target number of bytes if it is given a digest that is smaller than the target size already (instead of throwing an error)
2. it spreads the modulo bytes around rather than dumping them all into the final byte

Why is this better?
The old method divided the bytes into the target number of segments and after even division, placed all remainder bytes into the final segment. This meant that the effect of the remainder bytes on overall entropy was confined to the final byte.
In the new method, the remainder bytes are selected throughout the input bytes and are distributed evenly among the target segments, allowing them to express more entropy. The compression per input byte is more even, since the biggest difference in the number of input bytes per output byte is 1.

For example:

compress_old([123,456,798,147], 4)
# -> [123, 456, 789, 147]
compress_old([123,456,789,147,258,369,321],4)
# -> [123, 456, 789, 417] (only the last byte has changed)

compress_new([123,456,798,147], 4)
# -> [123, 456, 789, 147]
compress_new([123,456,789,147,258,369,321],4)
# -> [435, 902, 115, 321] (all 4 bytes have changed)

See also pull request on original repo: zacharyvoase#1

[coveralls]

Coverage decreased (-2.2%) to 97.826% when pulling e6dc5f7 on lafncow:master into 5bed9ac on blag:master.

[lafncow]

I've made a mistake in my git workflow that is causing PyPI work to bleed into my pull request on the original repo. To correct this, I am going to close this PR, branch my fork, and then create a new PR here. Sorry for the confusion.

[blag]

No worries! Do what ya gotta do.