No it  does not help....  

but it seems in data directory  everything has become number

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #000000; background-color: #ffffff} span.s1 {font-variant-ligatures: no-common-ligatures}

    p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #000000; background-color: #ffffff} span.s1 {font-variant-ligatures: no-common-ligatures}

data/caches

0fea6a13c52b4d47  1952a01898073d1e  views_simplecache

and under these two numbered folder  there are many numbered folders

By the way,,

I could get rid of my problem by renaming blog\classes\Elggblog.php to ElggBlog.php

Probably this is because the old classname in my GIT repo was Elggblog and not ElggBlog... 

so git silently ignored it..

The upper/lower cases of the classes names are important

Sorry My mistake...

There was some other plugin which was having start.php with extra line before <?php

Might be that mod_rewrite is not enabled on the server or that AllowOverride is not set to All in Apache's config. I don't know what else might be causing the problem.

I've been working on upgrading my site from elgg2.3.7 to 3.0.3 as well and this is what I learned so far. 

elgg_register_library is removed from elgg3.*. What I did with my plugins was using the word 'require' or 'require_once' inside init function in the start.php file of my plugin. Below is the example:

require elgg_get_plugins_path( ) . 'plugin_name/lib/library_name.php'; 

Read more here http://learn.elgg.org/en/stable/appendix/upgrade-notes/2.x-to-3.0.html?highlight=elgg_register_library

+1

Or move your code from library to start.php or classes

Let's say you have a library at mod/my_plugin/lib/my_lib.php. Then you can load it with the line

require_once(dirname(__FILE__) . '/lib/my_lib.php');

when adding this line at the top of start.php (not inside the init function). This is the easiest way if you don't want to use elgg_register/load_lib anymore (works not only on Elgg 3 but also on Elgg 2). The other way would be to rewrite the code to create a class from the library. But this requires more effort for sure.