Convert invalid hyphens to underscores for Android

[morewry]

Fixes #158.

According to the Android developers I work with, hyphens (-) are not valid in resource identifier names. I wasn't able to find an official, specific source verifying this, however, I noted that none of the resource examples https://developer.android.com/guide/topics/resources/providing-resources showed hyphens, while many showed underscores (_).

This answer on StackOverflow states that Android resource identifier names must conform to the rules for Java identifiers, which are restricted to letters, digits, underscore, and dollar sign:

The "Java letters" include uppercase and lowercase ASCII Latin letters A-Z (\u0041-\u005a), and a-z (\u0061-\u007a), and, for historical reasons, the ASCII dollar sign ($, or \u0024) and underscore (_, or \u005f). The dollar sign should be used only in mechanically generated source code or, rarely, to access pre-existing names on legacy systems. The underscore may be used in identifiers formed of two or more characters, but it cannot be used as a one-character identifier due to being a keyword.

The "Java digits" include the ASCII digits 0-9 (\u0030-\u0039).

My implementation approach is to specifically address hyphens as a common input and directly convert them to underscores in an attempt to preserve authorial intent. See #160

Normally, I would have added a test case for something like this, but see #161.

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @CH-RhyMoore to sign the Salesforce.com Contributor License Agreement.