Refactor SourceInfo into Source.

A Script object is associated with a Source object (HAS-A relation.)

A Source object describes the source code (more specifically, the LLVM
module) that is going to be compiled.

BCCContext contains the context used in a Source object.

BCCContext is now managed by the user not the libbcc itself. That is,
user should supply the context object when they create a Source object.

Change-Id: Icb8980d6f15cf30aa0415e69e3ae585d990dc156
16 files changed