Support resolving the latest sub-revision of a module

Components of revisions are separated by dots or hyphens.

In case you "end the revision with a `+`" (see [1]), the latest sub-revision of the
dependency module should be selected when resolving dependencies.

Accept revisions such as "1.2+" or "1.2.+" and "1.2.3-+".

Fixes #424.

[1]: http://ant.apache.org/ivy/history/latest-milestone/ivyfile/dependency.html

tests/shared/src/test/scala/coursier/test/VersionConstraintTests.scala

@@ -20,6 +20,10 @@ object VersionConstraintTests extends TestSuite {
         val c0 = Parse.versionConstraint("(,1.2]")
         assert(c0 == Some(VersionConstraint.interval(VersionInterval(None, Some(Version("1.2")), false, true))))
       }
+      'latestSubRevision{
+        val c0 = Parse.versionConstraint("1.2.3-+")
+        assert(c0 == Some(VersionConstraint.interval(VersionInterval(Some(Version("1.2.3")), Some(Version("1.2.4-a1")), true, false))))
+      }
     }
 
     'repr{