No way to load fonts

[AlexApps99]

The example for loading fonts in ImGui is only provided for imgui_glium_renderer. The example uses a method called reload_font_texture, which this library does not provide.

There are no examples on how to load a font in this renderer, and I'm sure loading fonts is an important feature to support.

At least 3 backends support it, while this one does not:
imgui_glium_renderer imgui_wgpu imgui_gfx_renderer

[AlexApps99]

Since this backend is very different to the three examples above, it might be worth redoing the API to make it closer.
It would make it easier to use when basing off the examples provided by imgui-rs, and make it easier to support multiple backends for a program.