Add support for --raw and --omit to js2c.

  --raw writes the raw source data to a separate file
  --omit allows omitting the source data from the generated files.

The intention is (future) support for having the embedder optionally
store the source data 'blob' and handling it to V8::Initialize, with
the goal of reducing the binary size of V8.

The patch also contains numerous unrelated changes/refactorings in the hope of increasing maintainability. Let me know whether you agree. In particular:
- Remove some unused code.
- Do not overwrite Python built-ins (e.g. the type() function)
- Do not use a string as exception object (no longer supported in python 2.7)
- Add command line argument handling + help text.
- Split logic into:
  - PrepareSources - which reads + preprocesses the source files
  - BuildMetadata - which takes the prepared sources and generates the data the code template needs.

BUG=355539
LOG=N
R=jochen@chromium.org

Review URL: https://codereview.chromium.org/225723002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20657 ce2b1a6d-e550-0410-aec6-3dcde31c8c00