Pr/tsconfig file configurable

[Knaackee]

For my project i need to use a different tsconfig.json for development and deployment. In order to do that, I extended serverless-plugin-typescript and added the ability to configure a path to a tsconfig.json. I already use this in production.

I also added tests and documentation (README.md).

[JackCuthbert]

Hi @Knaackee thanks for submitting this one! Do you feel that adding the custom.typeScript:tsconfigFilePath configuration is the best way to implement this functionality?

Perhaps we can make an assumption that if the developer has a tsconfig.json file in their directory we should use that instead of the built-in config? (with some validation and documentation of course)

Edit: Sorry, I misunderstood, it appears that the plugin does use a tsconfig.json in the root directory if it exists (ref). I think this would be a good thing to support, using different dev/prod tsconfigs is certainly a thing people do :) Would you be able to rebase your branch on master now there has been a few changes?

[KingDarBoja]

Any update on this? Looks like the author went MIA (missing in action) as there hasn't been a rebase with latest changes on master.

Maybe another PR which mirror the changes could do the job, just saying.