TemplateHaskell utility

• Add parseConfigSpecTH functionality, now we can parse the ConfigSpec
  record at compilation time (closes #47)
• Remove bug on CLI option parser, now it will coerce numbers and
  booleans to string when specifying numbers and booleans over CLI
  and the field type is a string (closes #48)
• Improve Error Types to be more granular and descriptive
• Re-organize Spec parser functions in its own module
• Add switch input for CLI spec (closes #41)