v0.2.0

This release of Garble drops support for Go 1.15.x, which is necessary for some
of the enhancements below:

• New: garble test allows running Go tests built with obfuscation
• New: garble reverse allows de-obfuscating output like stack traces
• Names of functions implemented in assembly are now obfuscated
• GOPRIVATE=* now works with packages like crypto/tls and embed
• garble build can now be used with many main packages at once
• -literals is more robust and now works on all of std

The README is also overhauled to be more helpful to first-time users.

Known bugs:

• obfuscating the entire standard library with GOPRIVATE=* is not well supported yet