Add fast approximations of x^2.4 and x^(1/2.4)

Use a chebyshev polynominal approximation of these to speed up
gamma conversion. Based on the post in:

http://stackoverflow.com/questions/6475373/optimizations-for-pow-with-const-non-integer-exponent/6478839#6478839

https://bugzilla.gnome.org/show_bug.cgi?id=678318
Use new approximations for gamma conversions

https://bugzilla.gnome.org/show_bug.cgi?id=678318
index-static.html.in: force utf-8 charset in <head>
index-static.html.in: correct usage example
* babl_fish return a const Babl*
* better naming
tests: add a test for conversions cairo-RGB24 <-> R'G'B' u8
babl: don't write anything if dest model lacks a source component

otherwise converting cairo-RGB24 to R'G'B' overwrites the red
component with the PAD.
extensions/gggl.c: move table-based conversions in #ifdef USE_TABLES

and the corresponding not using tables in the #else branch
extensions/gggl{,-lies}.c: reduce errors of table-based conversions

centering the sample within the range of floats it represents
extensions/gggl{,-lies}.c: fix conversions u16 <-> u8

u16 maximum value is 0x10000 - 1 == (0x100 - 1) (0x100 + 1)
u8 maximum value is 0x100 - 1
thus the direct conversion requires multiplication/division per
0x100+1

division per 0x100+1 is implemented using 1 term of (1 + x)^-1
MacLaurin expansion

(1+x)^-1 == 1 + (-1) x

a * (1 + 1/256)^-1 * (256^-1) == (a - a / 256) / 256

with integer division rounded toward the nearest.
extensions/gggl{,-lies}.c: use 'lrint' where it is not yet used

and instead of 'rint'.
'lrint' returning a long does not require a conversion double->int
that in theory requires changing the rounding direction from
toward the nearest to toward zero.
extensions/gggl{,-lies}.c: fix a Fixme: (>>8 vs /255)

division per 0x100-1 is implemented using 1 term of (1 + x)^-1
MacLaurin expansion

(1+x)^-1 == 1 + (-1) x

a * (1 - 1/256)^-1 * (256^-1) == (a + a / 256) / 256

with integer division rounded toward the nearest.
extensions/gggl{,-lies}.c: round toward nearest in integer unpremultiplication

from (docs/BablFishPath.html):
../extensions/.libs/gggl-lies.so 0: RaGaBaA u8 to RGBA u8
    error: 0.001425 cost: 81 processings: 1 pixels: 128
../extensions/.libs/gggl.so 0: R'aG'aB'aA u8 to R'G'B'A u8
    error: 0.001971 cost: 71 processings: 1 pixels: 128
../extensions/.libs/gggl.so 0: R'aG'aB'aA u8 to R'G'B' u8
    error: 0.001971 cost: 71 processings: 1 pixels: 128

to:
../extensions/.libs/gggl-lies.so 0: RaGaBaA u8 to RGBA u8
    error: 0.000031 cost: 81 processings: 1 pixels: 128
../extensions/.libs/gggl.so 0: R'aG'aB'aA u8 to R'G'B'A u8
    error: 0.000042 cost: 61 processings: 1 pixels: 128
../extensions/.libs/gggl.so 0: R'aG'aB'aA u8 to R'G'B' u8
    error: 0.000042 cost: 61 processings: 1 pixels: 128
extensions/gggl{,-lies}.c: do not register the same conversion twice or +

grep "o (" extensions/gggl.c | sort | uniq -d
grep "o (" extensions/gggl-lies.c | sort | uniq -d
Add simple test app to test pow-24 accuracy

https://bugzilla.gnome.org/show_bug.cgi?id=678318
Revert "extensions/gggl{,-lies}.c: do not register the same conversion twice or +"

This reverts commit bc66f5ae8a98896f360549cb87cbbfae77d176df

The conversions in gggl and gggl-lies are not the same, even though the lines
registering them seem identical; their effect is different since the same
names refer to different pixel formats. Further restructuring these
conversions and getting rid of the gggl legacy naming of them might be
beneficial..
Revert "Add simple test app to test pow-24 accuracy"

commit dc824c0ac704b35130aff44e544e8666e21b5bc5 which was pushed by accident.
Bug 673422 - Babl C type not accessible to introspection bindings

https://bugzilla.gnome.org/show_bug.cgi?id=673422
Annotate Babl C type to be Babl.Object in GIR using the
"rename to" annotation in GI 1.33.5+. For earlier versions,
use a static .gir file to achieve the same.
introspection: Babl.BablObject -> Babl.Object
extensions: add fastpath for R'G'B'A u8 to cairo-ARGB32 conversion
extensions: make fastpath for R'G'B'A u8 to cairo-ARGB32 have 0 error