Version 1.0

• #17 Add Exec provider that executes an executable and provides its output.
• #18 Add conditional providers under sub-namespaces String, Int and Bool:
  IF, EQ, NE, GT, GE, LT, LE, AND, OR, XOR, NOT.
• #19 Try to parse string values as int or bool, and provide *AsInt / *AsBool values on success.