deprecate tslint

[troy351]

What problem does this feature solve?

see palantir/tslint#4534

What does the proposed API look like?

[LinusBorg]

This will not be an immediate deprecation; on the contrary, there is a lot of work to do to ensure a smooth transition to the new tooling without any regressions.

We will not deprecate tslint before they do. Deprecating it would require us to tell people what to use instead, and directing them to use eslint-typescript now would leave them with a lot of missing functionality that they relied on from tslint.

We are tracking this situation and will deprecate tslint when the main project does, asuming they/we can ensure a decent alterntive path by then.