add support for powershell

[dxking]

This pull request adds support for PowerShell.

Logo was derived and modified from the existing zsh.ascii file. I'm not totally in love with the ASCII art but can't quite pin down what could improve it.

[spenserblack]

🤔 Perhaps you could use white text for the >_ to make it a bit more distinct from onefetch's zsh logo and closer to the official PowerShell logo. What do you think?

[dxking]

@spenserblack I made some changes to powershell.ascii to add white for the >_ and switched up the characters being used (nothing really seemed to go well with # that was being used for the background). I think it looks a bit better now.

[o2sh]

To be even closer to the original design, we may want to "lean" toward smth like that:

{0}         ########################
{0}        ####{1}####{0}################
{0}       ######{1}####{0}##############
{0}      ########{1}####{0}############
{0}     ##########{1}####{0}##########
{0}    #########{1}####{0}###########
{0}   ########{1}####{0}############
{0}  #######{1}####{0}#############
{0} ######{1}####{0}#####{1}######{0}###
{0}########################

What do you think @dxking ?

[dxking]

@o2sh Yeah, that looks great! I can get powershell.ascii updated with that design, thanks!

[dxking]

Updated to use your suggested ASCII art.