This is more or less a complete re-organization of the code.
* Use the actual byte size of the .bin file as the flash size,
as the algorithm for packing sections into the flash is complicated
* Match each section to a data region & find the high water mark in the
region
* Report on all the RAM regions, separately
Note that elftools is a requirement of esp-idf and so does not need to
be listed in our requirements.txt.
This detects an overflowed flash partition, such as
```
1452105 bytes used, -10313 bytes free in flash firmware space out of 1441792 bytes (1408.0kB).
444428 bytes used, 1652724 bytes free in ram for stack and heap out of 2097152 bytes (2048.0kB).
```
on a metro esp32-s2 built with debugging.
