Save palette colors to XPF and PNG

[kanurag94]

Type: Enhancement
Fixes #196

XPF file and PNG now contains palette colors. The colors are to be passed in hex format.
Sample xpf file:

;Position file automatically generated by XaoS 4.1
;  - a realtime interactive fractal zoomer
;Use xaos -loadpos <filename> to display it
(initstate)
(defaultpalette 0)
(palettecolors "ffffff" "fce94f" "180719" "c5421c" "1d120b" "872e47" "181b0d" "f1e680" "111f18" "f0a28b" "0b041e" "6a57bd" "1d150e" "0c8c76" "0a061d" "32904d" "160018" "94bcf3" "042007" "e7920e" "0a0d14" "b89344" "0d1c03" "a9f898" "040022" "3e5330" "071516" "9861b8" "08030c" "f75ceb" "1f2010")
(formula 'mandel)
(view -0.75 0 2.5 2.5)

Using Command Line:

xaos -palettecolors  "ffffff" "fce94f" "180719" "c5421c" "1d120b" "872e47" "181b0d" "f1e680" "111f18" "f0a28b" "0b041e" "6a57bd" "1d150e" "0c8c76" "0a061d" "32904d" "160018" "94bcf3" "042007" "e7920e" "0a0d14" "b89344" "0d1c03" "a9f898" "040022" "3e5330" "071516" "9861b8" "08030c" "f75ceb" "1f2010"

[kovzol]

Nice improvement, thanks!