Support complex expressions

[j8r]

Support complex expressions, like npm's semver implementation like "or" || and hyphen ranges.

I've implemented most of them with the npm's syntax in semantic_compare (caret ranges ^ instead of ~> and no space between the operator and version number)

[j8r]

To add some context: the Ruby inspired gem syntax can be kept, but the use case is when we support LTS versions of a library - we need an expression like ~> 1.2.0 || ~> 2.4.0

[ysbaddaden]

To be honest I never needed any of these.

1. forcing no space between operator and version makes no sense to me (arbitrary parsing rule).

2. I don't understand the || rule: multiple versions should restrict versions, not expand them arbitrarily. Furthermore Crystal ain't even aiming for a stable release, libraries even less, so long-term-support for libraries seems soooo far away.

3. The ^ constraint always confuses me, especially since one should never expect a minor version to never break (it will). I believe the ~> requirement is far more safe, along with an outdated command to easily search for outdated dependencies.

4. Shards doesn't require semver. It happens to support it, but doesn't enforce it in any way.

All in all, I believe an outdated command and supporting pre-release versions (see #184) would be more useful than supporting ^ or || for the time being.

[j8r]

I never said to port caret or tilde ranges, but having a way to have the "or" operator || and hyphen ranges. This way we can restrict versions between one to another, that are tested to work properly. A program works for versions after 1.2.9 until 1.4.7 for example, that is untested.

[ysbaddaden]

Superseded by #261