Add `Exploit.vulnerable_version?` and `#vulnerable_version?` methods

[postmodern]

Now that Exploit.software_versions returns an Array of Support::Software::VersionRange objects, it should be easy to determine if a given version is vulnerable or not. Two methods should be added:

• Exploit.vulnerable_version?
• Exploit#vulnerable_version?

[postmodern]

Impelemented by b42b5ec.