Add incrementVersion() with semver

[skypanther]

Implements Fokke's incrementVersion() function using semver. I changed this also to increment & save the android:versionName value, as that is the value seen by the user. To see this work with the android version attributes, uncomment the manifest tag in tiapp.xml. I left that commented out to show that the tests work with or without that tag.

[tonylukasavage]

#21 (comment)

[skypanther]

Not sure if you're just linking PRs with your comment or if I was meant to see something there specific.

My PR doesn't implement his CLI

I use semver and handle non-semver starting conditions (like the default 1.0 supplied in a stock tiapp.xml)

The choice of using incrementVersion() rather than setVersion() is specifically for use with grunt scripts like the one Fokke has published or mine.

[tonylukasavage]

My point was that I don't want to change the established API syntax for the sake of a separate external project. I'm pretty adamant about it being setVersion to adhere to this syntax. I would also prefer not pulling in semver or handling the version at all, mainly because it would break using our CI version numbers (i.e., 3.5.0.v20141028174916).

tiapp.xml is meant to be a clear programmatic interface to changing the tiapp.xml files. I don't want to introduce new syntax (like the patch/minor/major stuff) that doesn't have a direct parallel in the tiapp.xml, no additional abstraction level. These types of improvements seem like a better fit for grunt plugins or another module that extends this.