Add a method that determines the executable format of a file

[postmodern]

Add a method that determines the executable format of a given file. It should do this by opening the file, reading a few bytes, and determining the file format based on the magic bytes (ex: every ELF file starts with 7f 45 4c 46 or \x7fELF). This method will then be used to determine which file format parsing library to use in order to extract the .text section.