Various usability improvements

[jhol]

This patch-set makes a variety of usability improvements. The most significant of which are as follows:

Replaces the command line interface with verbs

Previously the different marlintool.sh actions were performed by different flags set by the user. This is problematic, because other flags are context-specific on various commands which makes the interface rather messy.

This patch-set contains changes this so that it is invoked with marlintool.sh VERB <arguments> - similar to the git command line interface.

Downloads are now cached

Some components are large and take a significant length of time to download on slow connections, which can make configuration of the marlintools.params file a time-consuming process.

This patch-set contains changes so that these downloaded files are stored in the .cache sub-directory.

[jhol]

@mmone did you get time to take a look at this yet?

[jhol]

@mmone Any interest in these patches?

[jhol]

bump?