[module] Use heap objects more consistently
[module] Simplify RequreFunction constructor
[module] Do not check for core modules twice
[module] Make use of NODE_CTX_V4 macro
[engine, module] Fix module caching
[buffer] Implement read(U)Int8/16BE/32BE() methods
[buffer] Provide read(U)Int16LE/32LE() functions

Also make use of Qt's built-in functions for endianness handling.