is_xid_start and is_xid_continue removed for public char api

[igalic]

Despite the fix following #7, a month later, with rustc 1.39.0-nightly (34e82a7b7 2019-09-10)
this fails again, for the same reason:

error[E0599]: no method named `is_xid_start` found for type `char` in the current scope
   --> /home/meena/.cargo/registry/src/github.1485827954.workers.dev-1ecc6299db9ec823/runtime-fmt-0.4.0/src/fmt_macros.rs:422:34
    |
422 |             Some(&(pos, c)) if c.is_xid_start() => {
    |                                  ^^^^^^^^^^^^ method not found in `char`

error[E0599]: no method named `is_xid_continue` found for type `char` in the current scope
   --> /home/meena/.cargo/registry/src/github.1485827954.workers.dev-1ecc6299db9ec823/runtime-fmt-0.4.0/src/fmt_macros.rs:431:18
    |
431 |             if c.is_xid_continue() {
    |                  ^^^^^^^^^^^^^^^ method not found in `char`

error: aborting due to 2 previous errors

[jebrosen]

Looks like rust-lang/rust#62848