Ability to set the source version to 'latest-snapshot'

[rs017991]

The existing 'latest' behaviour only works for releases, so I added a 'latest-snapshot' option which will result in the latest unique version of the latest snapshot.

Examples

Let's say you have the following unique versions of your artifact: 1.0.0-SNAPSHOT:

• 1.0.0-20170328.031519-19
• 1.0.0-20180429.041620-20

2.0.0-SNAPSHOT:

• 2.0.0-20190101.010101-01
• 2.0.0-20190202.020202-02

Then these are the results you will get by setting the source.version to the following values:

source.version	Resulting JSON
1.0.0-SNAPSHOT	[{"version": "1.0.0-20180429.041620-20"}]
2.0.0-SNAPSHOT	[{"version": "2.0.0-20190202.020202-02"}]
latest-snapshot	[{"version": "2.0.0-20190202.020202-02"}]