FR: Add CleanerML function to query a registry key (Windows)

[Nightblade]

Purpose:

To find out where the software to be cleaned is installed.

Example:

Assume the following registry entry:

Registry key: HKLM\SOFTWARE\WOW6432Node\Valve\Steam
Value: InstallPath
Data: F:\Games\Steam

CleanerML usage:

...
  <var name="install_dir">
    <value get.registry="HKLM\SOFTWARE\WOW6432Node\Valve\Steam\InstallPath"/>
  </var>
...
    <action command="delete" search="glob" path="$$install_dir$$\dumps\*.dmp"/>
...

Notes:

• Would probably make wishlist item FR: Add user-configurable "extra install locations" setting #108 unnecessary?