Include math.h

[jdavid]

SparkFunBME280.cpp uses math functions pow, log and log10. This produces
errors such as "pow was not declared in this scope". Found this while
packaging this library for RIOT-OS.

The library works with Arduino because math.h is included somewhere
else. But I think it's better or more correct to include the headers for
the functions used.

Fixes#48

[nseidle]

Shouldn't this be included in the header that includes the compile guards? Yes, math.h should have it's own guards but it's best practice to put math.h inside SparkFunBME280.h, no?

[jdavid]

A quick search for best practice makes me think it's the opposite: include where it's used, e.g. https://stackoverflow.com/a/3002124/9055637

But if you prefer I will move the include to the header file.

[jdavid]

e.g. in my cpp file I have:

#include <SparkFunBME280.h>

If #include <math.h> is in the header file then math.h will be included in my cpp file, increasing a little bit the work the compiler has to do.

[nseidle]

I stand corrected! Thank you for the education. It's a simple change but I'll test this out with the other PRs later this week.

[nseidle]

Thanks again!