ISO 286/14405-1 calls for a plus sign if the limit is positive and a
minus sign if the limit is negative. A zero limit should have neither
a plus nor a minus sign. This commit adds the plus sign.
- left justify tolerances
- use format spec for tolerance == zero
- prevent uncommanded tolerance format changes
- use 'w' format for HoleShaftFit
- allow zero tolerance values for HoleShaftFit
