Wider types for counts and offsets

Counts and offsets through Haskell code now use Int64, platform independent 64-bit integer.

C code receives counts and offsets in long values, also 64-bit for 64-bit platforms.

create-floats has special define to allow local testing. Compile with -DLOCAL_TEST and run with chunks count 1 and chunk number 0 to write a whole file at once.

Code has been tested locally and works.