Previously, parameter block reused the same syntax as in Idris1:
```
parameters (v1 : t1, … , vn : tn)
```
Unfortunately this syntax presents some issues:
- It does not allow to declare implicit parameters
- It does not allow to specify which multiplicity to use
- It is inconsistent with the syntax used for named arguments elsewhere
in the language.
This change fixes those three problems by borrowing the syntax for
declaring type parameters in records:
```
parameters (v1 : t2) (v2 : t2) … (vn : tn)
```
It also enables other features like multiple declarations of arguments
with the same type:
```
parameters (v1, v2 : Type)
```
