PyInfra: Provide a PowerShell drive

[Paebbels]

PowerShell has the ability to provide user-defined drives. PoC should provide a drive called poc. This allows fast access (and tab completion) to IP cores, testbenches and constraint files. Normal CmdLets like dir and cd could be used to browse PoC's IP core database.

Possible output:

dir poc:\io\ddrio

PoC Entity             Source file         VHDL name
----------------------------------------------------
Package ddrio          ddrio.pkg.vhdl      ddrio
PoC.io.ddrio.in        ddrio_in.vhdl       ddrio_in
PoC.io.ddrio.inout     ddrio_inout.vhdl    ddrio_inout
PoC.io.ddrio.out       ddrio_out.vhdl      ddrio_out