scritcs session state is now 'sticky' across calls to invoke-scriptcs
added unit test project; added indirection in current cmdlet context and implementation of null cmdlet context to cope with PowerShell pscmdlet object methods only working on cmdlets in active pipelines
merge nuget changes from master
added unit tests for cmdlet context stack operations; added cmdlet logger stack to invoke-scriptcs
ensure that current logger and current cmdletcontext are never null references
added cmdletname to cmdletlogger output; rev'ed assembly version number to 1.0.2