Auto detect total number of bits

[furkanusta]

Hi, I've added a feature to auto-detect the number of bits by summing all in the input file.

I wasn't sure whether to use a numeric default (e.g. -1, 0), a string default ('auto') or 'undefined' so I went with the last one.

I can open a PR if you are interested.

Here is the code if you want to check
63a46c3

[drom]

PR is welcome