v0.8.0-dev

• Add constructors: quat, mat4
• Add quat as a alias type of vec4
• Constructors: add error message when using if compiler does not support
• Constructors: overloading like GLSL
• Avoid .m128 usage simd, that cause unportable code on clang extensions
• Merge simd and clang implementation into one, remove vectormath_clang.h file
• Add docs: CONTRIBUTING.md, SECURITY.md, PULL_REQUEST_TEMPLATE.md
• Operators: temporary hide vec2 * mat4, mat4 * vec2, vec3 * mat4, mat4 * vec3. Maybe add a config later.