Unit Converter

You are required to build a simple web app that can convert between different units of measurement. It can convert units of length, weight, volume, area, temperature, and more. The user can input a value and select the units to convert from and to. The application will then display the converted value.

1. The user can input a value to convert.
2. The user can select the units to convert from and to.
3. The user can view the converted value.
4. The user can convert between different units of measurement like length, weight, temperature, etc (more given below).
5. Length: millimeter, centimeter, meter, kilometer, inch, foot, yard, mile.
6. Weight: milligram, gram, kilogram, ounce, pound.
7. Temperature: Celsius, Fahrenheit, Kelvin.