Input key to symbol map has been moved to C++
SchedulerJob#rate

Returns a normalized value
MouseMove#normalized_position
Text#refresh_size should check for nil font
Added YAML#load_file and YAML#save_file
Restored Input::MOD_* constants
Fixed Keyboard number symbols
Switched / with - in Base64 random

Slashes would cause problems when used for filenames
DataModel::Metal#each_field_with_value
DataModel::Metal.array size: n option
RenderContainer#clear_elements

Removes all elements from the container
DataModel::Metal field checks can now be controlled via ```validate_fields?```
More core extensions Object#presence, Hash#exclude, Hash#permit
Eventable#on now returns the listener object
Minor Text optimization

Store split lines in a variable to avoid splitting the string at render time
Bump mruby
Spritesheet now accepts a Texture on initialize

Spritesheet#initialize(texture, cell_width, cell_height)
Remove old freetype-gl
Updated submodules

Using freetype-gl from github
Remove core directory