PowerShell language updates

[NoahStahl]

Hi there, very impressive work on the project. While implementing this and testing against PowerShell, I found a couple discrepancies that I wanted to report back. Namely, I found that the language definition was incorrect for string escapes (use backtick instead of backslash), and didn't recognize block comments (<# comments #>). I was able to resolve with the following change, though I'm not 100% sure of the escapes portion:

scopes: { string: [ ["\"", "\"", ["""]], ["'", "'", ["\'"]] ], comment: [ ["#", "\n", null, true], ["<#", "#>", null, false] ] }