C Standard compliance failed

[qrp73]

Current code has some syntax tricks which have issue with C standard compliance. Please fix it. It's hard to merge all changes when this fix is not applied. Thanks.

The main issues are following:

1) implicit cast from void(*)() to void* Proposed solutions:

• explicit cast
• use unnamed union to store void pointer or function pointer at the same memory, but with different field name

2) struct field initializers are not compatible with C standard Proposed solution: use C standard struct field initializers:

config_t config = {
  .magic =              CONFIG_MAGIC,
  .dac_value =          1922,
  .grid_color =         0x1084,
 //...
};

3) Binary constants are not supported in C standard. Proposed solutions:

• use hex constants
• use header file with predefined constants starting from letter b to translate binary constants to hex: #define b10001010 0x8A

fix is already done in the following two changesets:

• https://github.com/ttrftech/NanoVNA/pull/48/commits/e1e5ca2a2e1f8292115ed6b31db2878854244a42
• https://github.com/ttrftech/NanoVNA/pull/48/commits/abdb025990ef0d97763db1a688f51ff431bc0008