Changes between releases 3.40 and 3.50

* correction of a bug in map2alm_iterative, when a mask is used in combination with iter_order > 0,
* addition of zbounds in alm2map, alm2map_der, alm2map_spin in order to simulate (faster) a signal on only a fraction of the sphere,
* introduction of apply_mask to apply an arbitrary mask and/or a latitude cut to a map,
* improved support for version 18 and more of Intel C and F90 compilers in configure script,
* edition to fitstools.F90 allowing a proper compilation with g95.

Version 3.50, 2018-12-10