First draft of new build script
First sources.json draft
Need to use an optional `package` field;
incase url's that don't put the file in the url.
This commit amends far more than I would have liked to.

working script will;
Remove existing folders named in the sources
Download the packages listed in sources.json
Extracts the above packages
deletes the downloaded package
Merge pull request #157 from Jackbennett/scripts

Getting the build script to a working state
Add registration for right-click on folder item; Add context-menu icon

Existing code registered right-click only for blank areas of the
Explorer window.  This change adds a menu item for right-clicking on a
folder in the file list.
Also adds the program's icon to help find it in a crowded context menu.
A better way to find string length
Adjusted the build script behavior

Removed some absolute path, and refactored the code so
it handles the nested folder archives
Removed unused function
Refactored mail download loop, better error handling
Adjusted the build script behavior

Removed some absolute path, and refactored the code so
it handles the nested folder archives
Removed unused function
Merge branch 'scripts' of https://github.com/bliker/cmder into scripts

Conflicts:
	scripts/build.ps1
In powershell you pretty much never want to use Write-Host, its output can't be redirected along the pipeline. You couldn't pipe this output to a logfile.
Error checking for 7z extraction
Silencing the output from 7z so I can actually see what else the script is
doing.
Adding some clearer dubugging info for cleaning up folders
merging in new additions to the pull request
Merge pull request #162 from Jackbennett/scripts

Minor changes for #152
Use HOME if already set.
CD to HOME by default.