allow renaming rules for C enums, structs, and typedefs

[nyurik]

Add utilities to rename, change case, and fix Rust code generated from the C headers.

Renamer implements a bindgen callback trait. It handles struct/enum/typedef type renames with a string->string hashmap. Additionally, it can rename the enum variant names by removing regex matches, and change identifier case to PascalCase to be consistent with the Rust canonical style.

This is a port of the https://crates.io/crates/bindgen_helpers into a built-in feature, as it is fairly difficult to maintain a standalone bindgen plugin due to numerous dependency-hell-ish issues I discovered when using it.

// true to enable debug output as warnings
let mut ren = Renamer::new(true);

// rename a single item, e.g. a struct, enum, or a typedef
ren.rename_item("my_struct", "MyStruct");

// rename an enum and its values
rename_enum!(
    ren,
    "my_enum" => "MyEnum", // rename the enum itself
    remove: "^I_SAID_",    // optionally any number of "remove" regexes
    remove: "_ENUM$",
    case: Pascal,          // optionally set case convert, defaults to "PascalCase"
    "MV_IT" => "Value1",   // rename a specific value after pattern removal
    "MV_IT2" => "Value2",  // more specific value renames
);

let bindings = Builder::default()
    // in real code, use .header("path/to/header.h")
    .header_contents("test.h", r#"
struct my_struct {
    int a;
};
enum my_enum {
	I_SAID_YES_ENUM,
	I_SAID_NO_ENUM,
	I_SAID_MV_IT_ENUM,
	I_SAID_MV_IT2_ENUM,
};
"#)
    .rustified_enum(ren.get_regex_str())
    .parse_callbacks(Box::new(ren))
    .generate().unwrap();
}

///////////  generated code

#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct MyStruct {
  pub a: ::std::os::raw::c_int,
}

#[repr(u32)]
#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
pub enum MyEnum {
  Yes = 0,
  No = 1,
  Value1 = 2,
  Value2 = 3,
}