Add (limited) columnization for message output

[nevinera]

Right now, the message output from normal logging mode is completely ragged, which makes it hard to read.

The file-paths could be quite long, but are at least likely not to vary a great deal; the tool names are uniformly short. But the rule-names could vary substantially - I'd suggest giving them a maximum column width, and letting them overflow past it, such that rows with really long rule names just bust their column and start their message-body in the wrong place. Probably 60 characters is a reasonable limit?

[nevinera]

Perhaps we should just go unix here, and support a tab-separated output (not true tsv), specifically intended to be fed into column -s $'\t' -t? Wish there were a simpler command to use, but column -t by default splits on whitespace, which is not ideal.

[nevinera]

Actually, this isn't going to help - the shapes are too varied. Instead, let's take a cue from git, and support a formatting string. Alongside '-n', let's take --message-format="%ABCDNAME%A.BNAME", where each sigil takes two values and a string.

• A is either l, r, indicating justification - will it be left- or right-justified? (If it's shorter than the column width, will it be padded on the right or the left?)
• B is one of b, e, or m ("beginning", "end", or "middle"), indicating that the last, first, or middle section of the value will be truncated if necessary.
• C is a color, one of "yellow", "red", "green", "blue", "cyan", or "none"
• D is numeric, the space the column will use (the string will be truncated to fit).
  • Accept the special value '0' meaning "don't truncate or pad" so we can represent the existing format.
  • negative numbers mean "do not pad, only limit"
• NAME is the name of the value to be placed in the column - allowed values are "tool", "loc", "path", "lines", "rule", "body"

For example --message-format="%lbred40tool %lmcyan20rule"