Luna Engine v0.6.1 Released.

The following changed are made in Luna Engine v0.6.1:

1. Rename all primitive types:
   1. int8, int16, int32, int64 to i8, i16, i32, i64.
   2. uint8, uint16, uint32, uint64 to u8, u16, u32, u64.
   3. float32, float64 to f32 and f64.
   4. size_t, ptrdiff_t to usize, isize.
2. Add c8, c16 and c32 primitive character types.
3. Replace the original Base module with Runtime module, which is taken from Luna Engine v0.8. The following changes are made due to this replacement:
   1. IAllocator and IHeap is discarded. get_module_allocator is discarded. Now all modules allocate memory from one global memory heap, which is accessed by memalloc, memfree, memrealloc, memnew and memdelete (#include <Runtime/Memory.hpp>).
   2. IString, IStringBuffer, IBlob and IBuffer are discarded. New non-reference types String and Blob are introduced to replace those interfaces. strlib submodule in Core module is discarded too.
   3. result_t is discarded, new errcode_t is introduced to replace result_t, along with a more scalable and robust error handling system.
   4. IName is discarded. The new non-reference type Name and new name system is introduced to replace IName.
   5. The original module system in Core is discarded and replaced by a new module system in Runtime. The new module system handles module initialization and closing order automatically, rather than requiring the user to initialize all modules manually in order when the application starts.
   6. The logging interface ILogger is discarded.
4. IVariant in Core module is discarded and replaced by the non-reference type Variant.
5. IError is Core module is discarded and replaced by the non-reference type Error.
6. All namespaces are renamed to Pascal case.
7. Remove Color aliasing for Float4, using Color as the namespace for build-in color options (for example Color::blue).
8. Add built-in support for HLSL shader compilation in Studio (requires CMake 3.20.1).