Check compatiblity with ~2 versions of node-semver

https://github.com/isaacs/node-semver/compare/be44bda%5E...40343cc

# WIP

 - [x] Add tests from node-semver
 - [x] Fix failing tests
 - [x] Implement `^` operator
 - [x] Ignore build tags (drop everything after `+`)
 - [x] Implement "loose"

# Tests

| Date          | # fail | # ok  | # ex |
| ---------------- | ------- | ------- | ------ |
| 2013-10-02 | 128   | 1064 | 0     |
| 2013-11-18 | 0      | 0       | 0     |