Vim script for automatically detecting indent settings

The original plugin (the one in the official Vim plugin repository) seems to be abandoned, so this is a fork of raymond-w-ko’s version, which has, among other things, much more robust detection of indentation style. His README said this:

I merged all the forks that I found were semi-reasonable in the GitHub network graph. This was done in less than 15 minutes, so expect bugs!

My fork’s additions:

• set 0 for shiftwidth and -1 for softtabstop when supported, to make it easier for users to manually change indentation
• treat a g:detectindent_preferred_expandtab 0 value as signifying a desired default of noexpandtab
• slightly better wording of verbose log messages
• various refactorings
• style and formatting fixes in code and documentation

Feel free to submit pull requests or file issues.