doxygen: fix typos and some wrong expressions in Edje and Eet API reference documentation.
Summary: I had fixed some typos and some wrong expressions, such as capital letters, singular, and orders of groups in Edje and Eet API reference doxygen.
Test Plan: Doxygen Revision
Reviewers: stefan, cedric, raster, Jaehyun_Cho, jpeg
Differential Revision: https://phab.enlightenment.org/D4666
Signed-off-by: Cedric BAIL <email@example.com>