Remove all controllable short options for CLI

[neocotic]

Currently, the following options are supported by the CLI:

-V, --version              output the version number
--no-color                 disables color output
-b, --base-url <url>       specify base URL to use for all relative URLs in SVG
-f, --filename <filename>  specify filename the for PNG output when processing STDIN
--height <value>           specify height for PNG
--scale <value>            specify scale to apply to dimensions [1]
--width <value>            specify width for PNG
-h, --help                 output usage information

To be future-proof and avoid confusion when adding more options (see #14), we should remove all short options within our control. This includes the following:

• -b
• -f

These will still be accessible via their long options (i.e. --base-url and --filename respectively), however, the short options will no longer work.

Obviously, this will be a breaking change.

[neocotic]

This change has been implemented in 81eed21 and will be included in the 0.3.0 release.