Update README.md

Add a link to documentation
Sepia filter implementation and sample.
Modified documentation.
File with the sample for sepia filter.
Check input image.
Parameters (hue, saturation, value) were removed.
Tests for sepia filter were written.
Replace tabs with whitespaces.
Test was modified.
Test was modified.
Test was removed.
Test was restored, interval [<v>-1,<v>+1] was set for hue, saturation and value.
Matrix initialization in the test for sepia effect.
Merge pull request #23 from valentina-kustikova/sepia_impl

Sepia implementation and sample
Fix sepia documentation
Merge pull request #24 from druzhkov-paul/sepia_documentation_fix

Sepia documentation fix
Help string in the sepia sample was modified.
Merge pull request #25 from valentina-kustikova/sepia_sample_fix

Help string in the sepia sample was modified.
Add 2 new files and modify photoeffects.hpp
edit merge conflict