Adding verbose **optional** property

[alipov]

I've started to use this plugin, and found that it doesn't support verbose mode.

jarjar queries for it in com.tonicsystems.jarjar.Main#process method:

public void process(File rulesFile, File inJar, File outJar) throws IOException {
  if (rulesFile == null || inJar == null || outJar == null) {
    throw new IllegalArgumentException("rulesFile, inJar, and outJar are required");
  }
  List<PatternElement> rules = RulesFileParser.parse(rulesFile);
  boolean verbose = Boolean.getBoolean("verbose");
  boolean skipManifest = Boolean.getBoolean("skipManifest");
  MainProcessor proc = new MainProcessor(rules, verbose, skipManifest);
  StandaloneJarProcessor.run(inJar, outJar, proc);
  proc.strip(outJar);
}

I noticed it queries for skipManifest as well, so I've added support for passing both verbose and skipManifest as optional properties (default is false for both).

Tested on a demo project. When passing the following configuration:

jarjar {
    jarJarFile '../../tools/jarjar-1.4.jar'
    rules = [
            'rule com.squareup.okhttp.** ext.com.squareup.okhttp.@1'
    ]
    srcExcludes = ['META-INF/**']
    outputName 'build_repackaged.jar'
    outputDir 'libs'
    ignoreJarJarResult false
    verbose true
}

jarjar runs in verbose mode (as expected):

$ ./gradlew clean build
:demo:clean
:demo:createRawFatJar
:demo:createRulesFile
:demo:runJarJarRemoved META-INF/MANIFEST.MF
Renamed com/squareup/okhttp/ -> ext/com/squareup/okhttp/
Renamed com/squareup/okhttp/Address.class -> ext/com/squareup/okhttp/Address.class
Renamed com/squareup/okhttp/Authenticator.class -> ext/com/squareup/okhttp/Authenticator.class
Renamed com/squareup/okhttp/Cache$1.class -> ext/com/squareup/okhttp/Cache$1.class
Renamed com/squareup/okhttp/Cache$2.class -> ext/com/squareup/okhttp/Cache$2.class
// ...
// redacted
// ...
:demo:preBuild
// ....

If/once merged and published, I'll update the documentation and demo project.

[alipov]

Just realized that skipManifest is just a special case of srcExcludes (all it does is exclude the META-INF/MANIFEST.MF file, which can already be done by srcExcludes).
I'll remove the skipManifest and update the PR.