Support customizing the methods included in messages in CLI

[jiaojiaodubai]

I am writing a browser extension script to parse the data returned the server.

In my application scenario, for those returned masses, I only need to use decode and toObject, but the current command line does not support selecting the required methods. In order to minimize the script size, I have to manually delete those redundant methods.

I would like to have some thing like:

pbjs -t static -toolsets=decode,toObject -o compiled.js file1.proto