Closes #463.

Better to allow the user to choose how to organize her project.

skip_ci.

Closes #318.

Updated installation notes.

The Command Line Tools may be installed right from Xcode.

Correcting path on 'pod push' description

Updating description for pod push with more detail about how it works.

- `spec lint` can now accept multiple files passed
  as arguments.
- the linter can work in environments with xcodebuild.
- Other misc improvements.

Managing spec-repos:

    [32m$ pod repo add NAME URL [BRANCH][0m

      Clones `URL' in the local spec-repos directory at `~/.cocoapods'. The
      remote can later be referred to by `NAME'.

    [32m$ pod repo update NAME[0m

      Updates the local clone of the spec-repo `NAME'. If `NAME' is omitted
      this will update all spec-repos in `~/.cocoapods'.

Options:

    --help       Show help information
    --silent     Print nothing
    --no-color   Print output without color
    --verbose    Print more information while working
    --version    Prints the version of CocoaPods.