Improve documentation of FileSystemTool.copyFile() builder.
Normalise path separators in Compiler output messages.

This makes cake output more easily testable.
Add helper function for finding platform's default compiler.

Available as cake.library.compilers.findDefaultCompiler().
First pass at cake integration testing system.

Added some simple tests for:
- FileSystemTool.copyFile()
- Building a C library
- Building a C++ program that uses a library