New Compilation API, part 1

- Distinguish between context bound scripts (Script) and context unbound scripts
(UnboundScript).
- Add ScriptCompiler (which will later contain functions for async compilation).

This is a breaking change, in particular, Script::New no longer exists (it is
replaced by ScriptCompiler::CompileUnbound). Script::Compile remains as a
backwards-compatible shorthand for ScriptCompiler::Compile.

Passing CompilerOptions with produce_data_to_cache = true doesn't do anything
yet; the only way to generate the data to cache is the old preparsing API. (To
be fixed in the next version.)

BUG=
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/186723005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19881 ce2b1a6d-e550-0410-aec6-3dcde31c8c00