Resolve "Cannot read CMYK jpeg images"

Closes #19

See merge request !31

Merge branch '19-cannot-read-cmyk-jpeg-images' of https://gitlab.idiap.ch/bob/bob.io.image into 19-cannot-read-cmyk-jpeg-images

Merge branch '19-cannot-read-cmyk-jpeg-images' of https://gitlab.idiap.ch/bob/bob.io.image into 19-cannot-read-cmyk-jpeg-images

Add a utility function to convert images from matplotlib format to bob format

See merge request !32

fixed docs badge urls, see bob/admin#2

See merge request !30

Mention about bob.io.base.peek in user guide.

Closes #24

See merge request !29

Fixes #24

Merge branch '27-non-templated-functions-implemented-in-header-files-need-to-be-inlined' into 'master'

inlined non-templated functions implemented in header

Closes #27

See merge request !28

Moved test function into its own extension

Closes #23

See merge request !27

modified README, updated conf.py

See merge request !26

improve the imshow function to return the output of plt.imshow

See merge request !25

Fixes gcc-4.2.1+libstdc++ compatibility (closes #25)

Closes #25

See merge request !23

Resolve "16 bit PNG images are stored as big endian"

Closes #21 

I have added functionality to read and write 16 bit PNG images correctly. 16 bit PNG images are stored as big-endian, but before we were writing them as little-endian. This PR fixes that. 

This fix also includes a generic way of loading in one data type (e.g., uint_16) and automatically converting it into another data type (e.g., using uint8_t). Conversion is done such that pixel values are automatically scaled (in contrast to casting, which would cut off the MSB).

@andre.anjos I assign this PR to you since you have written the IO libraries.

See merge request !21

Merge branch '21-16-bit-png-images-are-stored-as-big-endian' of https://gitlab.idiap.ch/bob/bob.io.image into 21-16-bit-png-images-are-stored-as-big-endian

Fixed implementation of 16 to 8 bit PNG (now I am converting, instead of casting -> I get the MSB instead of the LSB)