Add core_3d_camera_first_person example

[nawarian]

• Transalte 3D example from C to PHP
• Test new methods
• Update README.md
• Figure out why movement isn't working
• Raylib::updateCamera() segfaults if FFI::addr() is returned from another method (Will be followed up by Raylib::updateCamera() segfaults if FFI::addr() is returned from another method #9)
• Fix issue: viewport behaves weirdly on my other machine (Will be followed up by Fix viewport issues with Camera2D and Camera3D #8)

[nawarian]

Fix issue: viewport behaves weirdly on my other machine

Seems like this is a general issue with Camera2D and Camera3D modes. Will be followed up by #8.

[nawarian]

The FFI::addr() issue found here is PHP-specific and will be followed up by #9