Math: Add lcm and gcd
Merge pull request #208 from aomoriringo/master

Math: Add lcm and gcd
Math: Fix gcd about 0
Math: doc: add empty line
Math: doc: fix typo
Merge pull request #209 from aomoriringo/master

Math: Fix gcd about 0
OptionParser: Refactorings

- rename *_completion to complete_*
- unify arguments; use arglead, cmdline and cursorpos
OptionParser: Complete user specified values on greedy completion