Invalid crate type should helpfully suggest valid crate type

[Havvy]

Errornous code: _{Yes, it's only a single line}

#![crate_type = "proc_macro"]

Current output:

   Compiling playground v0.0.1 (file:///playground)
error: invalid `crate_type` value
 --> src/lib.rs:1:1
  |
1 | #![crate_type = "proc_macro"]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[deny(unknown_crate_types)] on by default

error: aborting due to previous error

error: Could not compile `playground`.

Expected:

   Compiling playground v0.0.1 (file:///playground)
error: invalid `crate_type` value
 --> src/lib.rs:1:1
  |
1 | #![crate_type = "proc_macro"]
  |                 ^^^^^^^^^^^^ did you mean "proc-macro"?
  |
  = note: #[deny(unknown_crate_types)] on by default

error: aborting due to previous error

error: Could not compile `playground`.

The change here is that the error is on the value of the attribute and it asks the "did you mean" question that you get when you mistype a variable.

[phansch]

I would like to work on this.

From a first look, I would re-use

rust/src/libsyntax/util/lev_distance.rs

Line 50 in b7c6e8f

pub fn find_best_match_for_name<'a, T>(iter_names: T,

somewhere around here:

rust/src/librustc_driver/driver.rs

Lines 1476 to 1481 in b7c6e8f

	session.buffer_lint(
	lint::builtin::UNKNOWN_CRATE_TYPES,
	ast::CRATE_NODE_ID,
	a.span,
	"invalid `crate_type` value",
	);