Add option to use custom TypeScript compiler version

[rostacik]

Hi all.
First of all, thank you for this plugin, it really helps us to get-shit-done on our project.

Currently I have one small request though. I need to compile with TypeScript@next - nightly packages of TypeScript (http://blogs.msdn.com/b/typescript/archive/2015/07/27/introducing-typescript-nightlies.aspx).

I need to use --experimentalAsyncFunctions switch. I patched the package.json of your grunt-typescript and I compile against latest TypeScript after npm update I am with typescript@1.6.0-dev.20150818 currently and it all works well but I still have this error when using async/await in my .ts files (also patching tsconfig.json didn't helped) :

my_file_here.ts(line_numer,column_number): error TS1236: Experimental support for async functions is a feature that is subject to change in a future release. Specify '--experimentalAsyncFunctions' to remove this warning.

Thanx gents 👍

[sshaw]

@rostacik I had a similar problem, switched to grunt-ts as it allows one to specify tsc.

[rostacik]

thanks @sshaw , looks like we have to go this way :)