Modernizations and strictness improvements

[cgzones]

• modernize the codebase by using modern C++ features
• be more const-correct by using adjusting casts and enable -Wcast-qual
• declare more read-only functions const
• avoid value truncations in multiple places
• avoid out-of-bounds memory access and integer overflows on malicious ELF data

[Mic92]

Thank. Very appreciated. bors merge

[Mic92]

bors merge

[bors[bot]]

Build succeeded:

• Build static musl binaries (amd64)
• Build static musl binaries (arm32v7)
• Build static musl binaries (arm64v8)
• Build static musl binaries (i386)
• Build static musl binaries (ppc64le)
• Build static musl binaries (riscv64)
• Build static musl binaries (s390x)
• Build tarballs
• Build windows executable
• nix
• Test windows binaries
• ubuntu