More robust indentation detect algorithm

[franko]

I propose a new more robust algorithm to detect the indentation size. It reads the whole file and is not fooled if a few lines use a wrong indentation. It works by looking the distribution of indentation size and use a simple heuristics to determine the best guess.

I found it useful for files where the indentation size is not strictly respected.

[quadroli]

Just a comment, kinda intrusive how it overrides my initially set tab width, but nevertheless, cool upgrade

[franko]

I am open to amend its behavior if you have a suggestion.

[quadroli]

nah, not really, just wanted to point that out, some people are really religious over their tab lengths