fix casesensitive headers and invalid char conversions

[hpsaturn]

It fixed Invalid conversion from 'const char*' to 'char*' [-fpermissive]

[matthijskooijman]

I'm not sure I understand the last commit. It seems to revert the earlier commit, reverting unsigned char back to char. For me (AVR-based Arduino), the last commit breaks compilation again. With d0de9b637924c81c805a98118bc7559c07e28340 it works, with 0ac58d940d92aa65e0531f141247bf3991192ebf I get:

   hpma115S0.cpp: In member function 'boolean HPMA115S0::ReadParticleMeasurement(unsigned int*, unsigned int*)':
   hpma115S0.cpp:117:42: error: narrowing conversion of '147' from 'int' to 'char' inside { } [-Wnarrowing]
      char cmdBuf[] = {0x68, 0x01, 0x04, 0x93};

(and a few more of the same one)

In any case, this is about binary data, so it would seem sensible to use unsigned char everywhere rather than char?

[AlexFBP]

Please check if the hpsaturn fork works for you, @matthijskooijman .

[AlexFBP]

@hpsaturn may you do a fast forward in your branch fix_esp32? I marked #11 as duplicate... most of comits came from you and I requested you this pull you aplied in your fork haha