Throwable interface and its implementation (Exception structs) with stacktrace information in Go.

Eli Cox 68a6ebdde9 Test passes. %!s(int64=6) %!d(string=hai) anos
LICENSE 075c0502c0 Add LICENSE: public domain. %!s(int64=6) %!d(string=hai) anos
exception.go 68a6ebdde9 Test passes. %!s(int64=6) %!d(string=hai) anos
exception_test.go 68a6ebdde9 Test passes. %!s(int64=6) %!d(string=hai) anos
null.go 68a6ebdde9 Test passes. %!s(int64=6) %!d(string=hai) anos
null_test.go 68a6ebdde9 Test passes. %!s(int64=6) %!d(string=hai) anos
throwable.go 68a6ebdde9 Test passes. %!s(int64=6) %!d(string=hai) anos