Update prtgshell.psm1

Overhaul.
Added Get-PrtgSensorChannels

Might should cast "lastvalue_raw" to double before returning
Create custom_prtg_reports.ps1
Added Get-PrtgTableData
Notes on Get-PrtgSensorHistoricData

# todo:
#   adjust "avg" value, which sets the interval of data returned
#   included timestamp on each line of returned data
Added lastvalue_raw format error detector/handler

handler added to in Get-PrtgSensorChannels, needs to be updated in other functions as well
Update of Get-PrtgTableData and associated functions
Merge pull request #1 from sandersjds/patch-1

Update prtgshell.psm1