Various functions for creating spherical coordinate system plots via extensions to rgl.
Not released on CRAN.
CRAN legal- passed all checks.
rgl.sphgrid label now display properly- previously they was a radians/ degrees mismatch.
Major circles of 0 long and 0 lat are now a slightly darker grey for clarity.
Can now specify the colour of longitude and latitude labels.
car2sph wasn't working properly when matrices of xyz were being passed. Now fixed.
Package name in the manual was given as celsphere, changed to sphereplot.
Added the option of creating great circles on rgl.sphgrid.
Added option to plot ecliptic plane + Sun's location.
Added option to plot Galactic plane + MW centre.
Changed default coordinate type to degrees throughout (was a mix before).
Added radius label and vector.
Fixed the pointing latitude limits (these weren't being passed correctly previously)