chore: Rename NANODBC_H to NANODBC_NANODBC_H (#320)
chore: Rename NANODBC_H to NANODBC_NANODBC_H (#320)

Use `<LIBRARY NAME>_<HEADER NAME>_H` convention
for naming include guards to make things clearer
when new headers arrive.
nanodbc/nanodbc,nanodbc/nanodbc