Usability improvements for non-crate mode

[therealprof]

Taken from @therealprof in #147 (comment)

The issues noted here can be seen from: stm32-rs/stm32f4xx-hal#159 (comment)

It doesn't quite yield the expected output though. ;)

This is the human-readable output:

File  .text   Size         Crate Name
0.3%  39.2% 1.2KiB    dwt_blinky dwt_blinky::__cortex_m_rt_main
0.3%  36.9% 1.1KiB           std __udivmoddi4
0.0%   5.2%   158B           std __aeabi_memset4
0.0%   3.9%   116B   cortex_m_rt Reset
0.0%   3.3%   100B stm32f4xx_hal stm32f4xx_hal::dwt::Delay::delay_ticks
0.0%   3.2%    96B           std __aeabi_memset
0.0%   2.4%    72B stm32f4xx_hal stm32f4xx_hal::dwt::StopWatch::lap_time
0.0%   1.6%    48B stm32f4xx_hal core::iter::traits::iterator::Iterator::min_by_key::key::{{closure}}
0.0%   0.7%    22B           std __aeabi_uldivmod
0.0%   0.3%    10B   cortex_m_rt ResetTrampoline
0.0%   0.3%    10B           std core::panicking::panic_fmt
0.0%   0.3%    10B           std core::panicking::panic_bounds_check
0.0%   0.3%    10B           std core::panicking::panic
0.0%   0.3%    10B     [Unknown] main
0.0%   0.2%     6B           std __aeabi_memclr4
0.0%   0.1%     2B   cortex_m_rt HardFault_
0.0%   0.1%     2B    panic_halt rust_begin_unwind
0.0%   0.1%     2B   cortex_m_rt DefaultPreInit
0.0%   0.1%     2B   cortex_m_rt DefaultHandler_
0.0%   0.0%     0B               And 0 smaller methods. Use -n N to show more.
0.9% 100.0% 2.9KiB               .text section size, the file size is 342.6KiB

Few things of note:

• The toolchain is running on stable-x86_64-unknown-linux-gnu but the target is thumbv7em-none-eabihf (I would said the target is more important to know than the host architecture)
• @@ Breakdown per crate @@ should probably be @@ Breakdown per function @@ if the function mode is enabled
• It only lists the first two functions?
• While the total file size might be interesting every now and the really interesting metric here is the code (or .text) size, the complete file size also contains debugging information and other data which may not even end up in memory when running the binary