Adds a CPU-cache performance test. The libprof measure is extended into
Iϕ cycles (resolution: 16 Iϕ cycles) to check the 2-ILP parallelism
hypothesis (confirmed on fx-9860G and fx-CG 50).

The time needed to traverse a small buffer multiple times is also
measured with the same method in an attempt to determine cache size. No
definite result could be obtained.

This change includes a plotting utility.

Same in the hexadecimal memory browser, although there are currently no
shortcuts and it appears to freeze when leaving the add-in.

These are now called with TLB misses enabled, so there is no need to map
them constantly.

Somehow found by Kbd2 and better than my attempts.

* Added the switch menu
* Added the keyboard menu on fx-CG 50
* Added a (currently unused) bold 8x9 font on fx-CG 50
* Displayed something decent in the "Image Rendering" test on fx-CG 50
* Changed F-keys all around to unify the semantics
* Improved the layout of the RAM detection test
* Adapted TMU/ETMU display to the new mpu/timer.h definitions
* Added a timer selector in the F-key bar in the timer test
* Added an "external libraries" tab that will also test libc features
* Added a libimg test