Function htmIndex( level, ra, dec )

Description:
Gives the HTM (Hierachical Triangular Mesh) pixel index for a given sky position.
Parameters:
level (integer)
HTM level
ra (floating point)
right ascension in degrees
dec (floating point)
declination in degrees
Return Value (long integer):
pixel index
Signature:
long htmIndex(int, double, double)