New feature: overloadt but macro+layer instead of layer

[nazya]

Hi @rvaiya
I implemented a new feature called overloadtm, that additionally executes a supplied macro when activating a layer. If this feature belongs in keyd I'd like to make a PR. I implemented it as a 3 args descriptor (layer, macro, action) with a timeout defined in the global section.
Would be glad to hear you comments and make necessary changes / discuss my use case.