Release v0.5.0

Features in v0.5.0:

Type aliases:

alias := int

x: alias = 1

and, xor, and or boolean operators:

x := true and true
y := false xor true
z := true or false

is operator:

x := 1 is 2

Allow for escaped quotes in strings and runes:

c := '\"'
s := "what\'s your name?"

Multi-parameter functions:

f(a: int, b: int) int {
  return a + b
}

x := f(1, 2)

Else if statments:

if false {
  # do something
}
elif true {
  # do something else
}

Add line / column numbers for compiler errors:

$ cat file.sk
x := 1 + 2.0

$ skull file.sk
Compilation error: line 1 column 10: type mismatch: expected type "int"