evas: make the high level documentation more concise

evas: make the high level documentation more concise

Summary:
This is a very informative document but is much longer than it needs to
be.  Tighten it up by condensing redundant information and expressing
the ideas more efficiently.  Focus more on Evas and what it is than what
it isn't.  Avoid explaining general graphics concepts like immediate
vs. retained, replacing with synopses.  Switch from 2nd person to 3rd
person (i.e. don't say You/Your) to be less awkward, since we don't
really know why the reader is reading it.  Simplify the compilation
directions; these are pretty standard, and most people won't be manually
linking to Evas anyway.

While this shortens the document considerably, it retains the
important key points, and makes it far more readable.

Reviewers: cedric

Reviewed By: cedric

Subscribers: jpeg

Differential Revision: https://phab.enlightenment.org/D5130

Signed-off-by: Cedric BAIL <cedric@osg.samsung.com>