1. cleaning fuzz test crashes by removing some unwrap(), add slice boundary checks and using saturating_* functions.
2. reorganize some structs. elf_header, program_header and section_header mods are now standalone raw data structure, while the counterparts in elf mod contains reference for the whole ELF file for section content retrieval.
3. bump version to 0.3.0 as API changes.

• Commit 3ec9935
• Compare v0.3.0
• Tag v0.3.0

Vincent Hou