carrier 0.2.0

• crate() gains a .parent_env argument. The default is baseenv() in order
  to isolate the crate from the global search path. You can now set it to
  another environment. For instance, set it to globalenv() to make your crate
  inherit from the search path. Note that, as the global environment is
  serialized by name rather than by value, the crate is still isolated from
  objects in the global environment (#16).

• crate() now requires all ... arguments to be named instead of silently
  dropping unnamed arguments (#15).

• crate() gains .error_arg and .error_call arguments to allow for better
  error messages when calling crate() from other functions (#14).