Fixed compilation file paths and updated gitignore.

- Notation's "Build Phases" contained references to NotationTests that
  it did not need and caused compile-time errors. These have been
  removed.
- The path to the prefix-header file, Notation-Prefix.pch, has been
  updated in the "Build Settings" for both the Notation and
  NotationTests targets.
- .gitignore has been updated to ignore command-line build files.

Signed-off-by: Byron Sanchez <bfs5030@gmail.com>