Add support for instance calls

[BastianBlokland]

Add support for providing the first argument for a function on the left hand side ([firstArg].funcName([otherArgs]).

fun double(int i)
  i * 2

print(i = 42; i.double())

A more complicated example:

struct None
union Option{T} = T, None

fun string{T}(Option{T} o)
  o is T v ? v.string() : "none"

fun isDigit(char c)
  c >= '0' && c <= '9'

fun parseInt(char c)  -> Option{int}
  if c.isDigit()  -> int(c) - '0'
  else            -> None()

fun parseInt(string str)
  str.parseIntImpl(0, 0)

fun parseIntImpl(string str, int idx, int ac) -> Option{int}
  if idx >= str.length()           -> idx == 0 ? None() : ac
  if str[idx].parseInt() is int v  -> str.parseIntImpl(idx + 1, ac * 10 + v)
  else                             -> None()

print("1337".parseInt().string()      + '\n') // Output: 1337
print("13a37".parseInt().string()     + '\n') // Output: none
print("001".parseInt().string()       + '\n') // Output: 1
print("21232345".parseInt().string()  + '\n') // Output: 21232345
print("".parseInt().string()          + '\n') // Output: none