Fix and correct sentence in Base.ccall_macro_parse

[udohjeremiah]

The current doc for Base.ccall_macro_parse says:

"""
    ccall_macro_parse(expression)

`ccall_macro_parse` is an implementation detail of `@ccall

it takes an expression like `:(printf("%d"::Cstring, value::Cuint)::Cvoid)`
returns: a tuple of `(function_name, return_type, arg_types, args)`

The above input outputs this:

    (:printf, :Cvoid, [:Cstring, :Cuint], ["%d", :value])
"""

This PR complete the code block of `@ccall to `@ccall`, adds a period (.) to it to close that sentence. And then starts the next sentence with a capital letter.