See !18 for more.

The current rust nightly (rustc 1.30.0-nightly (33b923fd4 2018-08-18))
give us a warning for each test:

the feature `use_extern_macros` has been stable since 1.30.0 and no
longer requires an attribute to enable

So we don't need this anymore.

See !17 for more.

update proc macros2, add proc_macro_diagnostics, remove #![feature(proc_macros)] since it's stable in 1.29

We'll remove the minor version so Cargo picks up the latest ones...

https://github.com/rust-lang/rust/pull/50820

Depending on the kind of Ty (a Rust type we know how to Glib-ify), we
need to be able to create a GParamSpec with g_param_spec_int(),
g_param_spec_bool(), etc.

This commit adds these methods:

  Ty::to_gparam_spec_constructor
  Ty::to_gparam_spec_min_max_default

which are then used in properties.rs.

lib.rs: Be explicit about the proc_macro::TokenStream input/output vs. proc_macro2::TokenStream for internal work

parser/mod.rs: Take proc_macro::TokenStream from the compiler; handle proc_macro2::TokenStream internally

Since quote 0.6.2, the quote! macro generates tokens with
Span::call_site(), which is what we wanted.

I'm taking bets on whether proc_macro2 changes this again.

Also, introduce Names.exported_fn_from_str() to take that case into account.

Changed syn::Ident and proc_macro2::Term to proc_macro2::Ident
Changed quote::Tokens to proc_macro2::TokenStream
Deleted proc_macro::TokenStream where proc_macro2::TokenStream was added (this might have been a mistake)