[Enhancement] Provide a generic helper for manipulating segmented environment variables

[jberezanski]

There are several popular environment variables that are PATH-like in nature, i.e. their values consist of segments separated by delimiters.

Examples include: PSModulePath, PATHEXT, INCLUDE, LIB, CMAKE_PREFIX_PATH, CLASSPATH

I envision an Install-ChocolateyEnvironmentVariableSegment helper that would take the variable name, the delimiter character and the segment to add. It would, in essence, be a generalization of Install-ChocolateyPath.