Enable use in subprojects

[Joaquimmnetto]

Description

This plugin is no longer limited to the root project. On each project the plugin applies its version to all its child projects. This way, child projects without the plugin receives the version of the nearest parent with an applied plugin.

For instance, in the example below, projectA, subproject2 and projectC don't apply net.wooga.version, so their version are determined by the closest parent who does.

rootProject applies v4.0.0      -> rootProject.version == 4.0.0
├── subproject1 applies v1.0.0  -> subproject1.version == 1.0.0
│   ├── projectA (no apply)     -> projectA.version == subproject1.version == 1.0.0
│   └── projectB applies v0.0.1 -> projectB.version == 0.0.1
└── subproject2 (no apply)      -> subproject2.version == rootProject.version == 4.0.0
    ├── projectC (no apply)     -> projectC.version == rootProject.version == 4.0.0 
    └── projectD applies v2.1.0 -> projectD.version = 2.1.0

In projectA case it inherits its version from subproject1 and subproject2 and projectC inherits their version from rootProject. If there is no such available parent, no version is applied.

In meanwhile, rootProject, projectB and projectD apply their own net.wooga.version and so the inherited version is overwritten with the one generated by their own plugin instance.

Based on #60 , please merge that first.

Changes

• enable use in gradle subprojects