Add tagui_location() to support setting custom TagUI installation directory [done]

By default, the package installs TagUI to %APPDATA%/tagui folder for Windows, and ~/.tagui folder for Mac and Linux.

PR #207 by @fi-do will add option for users to specify where to install and where to find the installation to init() the tool.

To review to see if that can be implemented as a separate function or to provide as parameter to existing functions.