spiro.h is installed to /usr/local/include, but is missing spiro_seg info

Moved spiro_seg definition from spiro.c into spiro.h
libspiro 2007 installs spiro.h, which implies that run_spiro() and other
routines are also available, but those routines require info describing
spiro_seg to use them - which was not included in spiro.h
This opens up libspiro for developers trying to make use of internal
routines for something libspiro can't normally do using spiroentrypoints.h