Select2 Bootstrap 5 Theme v1.3.0

• Rewrote the docs, with more examples AND code examples!
• Fixed issues with Select2 sizing #57
• Fixed z-index issue in modals #61
• Removed form element requirement from validation selector #60
• Fixed some minor parity issues with Bootstrap
• Improved borders
• Set overflow on dropdowns to hidden to prevent option backgrounds breaking border radius
• Replaced gulp-dart-sass with gulp-sass
• Improved compiling process
• Add correct border radius to small and large sized fields
• Set color and background-color on dropdowns for improved theming