Treat negative numbers and dashes as values

[eush77]

Why is it a good idea?

• - is a special argument across multiple Unix commands and usually stands for stdin (echo hello |cat - /another/file);
• negative numbers are not usually expected to behave as options, but rather as values, this is also sort of a standard (echo -e 'hello\nworld' |head -1);
• I doubt there exists a single program which defines an option with spaces in it.

This patch is a superset of #38.

[jpb]

@eush77 what is the stats of this? I'm interested in using - to denote "read from stdin"

[eush77]

I rebased and squashed my changes into a single commit.

@harthur Is it ready to merge?