Documentation

First PR for documentation:

Start documentation for:

• erosion #9
• dilation #9
• opening #9
• closing #9
• hit or miss #9
• opening by reconstruction #10 (closed)
• closing by reconstruction #10 (closed)

See documentation in:

http://buildfarm.lrde.epita.fr/project.html?projectId=Olena_Pylene&branch_Olena_Pylene=development%2Fdoc-erosion