Allow BlitzMax variables in native code

[woollybah]

Currently, native code (inline C) can't directly interact with BlitzMax code, because we don't have a way to refer to BlitzMax variables within the native statements.

We can't use variable as-is in the native code, because the actual generated variable names are different. So, for example, we can't do this :

SuperStrict
Framework BRL.Standardio

Local a:Int = 10

'! printf("a = %d\n", a);
Print "a = " + a

because a in the native section is an unknown variable.

We may be able to prefix the variable in the native code, parse it, and check it during the semanting phase. The @ symbol seems a reasonable choice as it is not used in C. So we could end up with something like :

SuperStrict
Framework BRL.Standardio

Local a:Int = 10

'! printf("a = %d\n", @a);
Print "a = " + a

where @a would be replaced by the correct variable name during generation.