v0.4.0

• Suppress empty line when ghcmod#type() fails
• Disable :GhcModType and :GhcModTypeInsert if the current buffer is modified
  • Add new variant :GhcModType! and :GhcModTypeInsert! which is executed even if the current buffer is modified.
  • Change ghcmod#type() and ghcmod#type_insert() to take an argument determining the behavior when the buffer is modified.
• Fix ghcmod#detect_module() to detect the module name more correctly
• Change the default directory to execute ghc-mod from (@drchaos, #25)