Lift restriction on the function contains

[AlexanderLieret]

The function contains only allowed to check maps of the type map[string]string. This PR lifts this restriction and allows for arbitrary types to be used.

[buchdag]

@AlexanderLieret maybe the test unit should also be declined for other basic go types like bool, uint and float32 ?

[AlexanderLieret]

@buchdag I don't have much experience with go. This was a simple test to test what happens if a wrong key datatype is supplied.

I bit of testing revealed that the types of the keys are compared first. Checking with other types should not be necessary.

m := map[int]bool { 42: true }
m[42] // true
m[42.0] // true
m["42"] // compiler error
m[m] // compiler error
contains(m, 42) // true
contains(m, 42.0) // false
contains(m, "42") // false
contains(m, m) // false