write_fmt is adding a lot of memory overhead

[RJ-Russell]

Pretty sure the core formatting module is pulling in a lot of extra code that is adding ~7k to the total flash memory when compiling with: make release
Both examples are with the same commit: 940b93e

with write_fmt in panic handler commented out:

Compiling altos_rust v0.1.0 (file:///home/reaper6/AltOS-Rust/altos-rust/altos-rust)

    Finished release [optimized] target(s) in 1.6 secs
   text	   data	    bss	    dec	    hex	filename
   9020	    104	     44	   9168	   23d0	build/release/altos_rust
   9020	    104	     44	   9168	   23d0	(TOTALS)

with write_fmt in panic handler not commented:

Compiling altos_rust v0.1.0 (file:///home/reaper6/AltOS-Rust/altos-rust/altos-rust)

    Finished release [optimized] target(s) in 1.12 secs
   text	   data	    bss	    dec	    hex	filename
  15744	    104	     44	  15892	   3e14	build/release/altos_rust
  15744	    104	     44	  15892	   3e14	(TOTALS)