Internal restructuring, multi monitor fix

[1.1.0] - 2020-02-10

Changed

• Switch to u32 rather than [u8; 4] for most operations
• Refactor into more separate compile units
• Switch from SysV SHM to Linux SHM

Added

• Multithreaded brightness adjustment
• Nearest-neighbor scaling

• SHA256SUMS: SHA256 checksums of all files
• SHA256SUMS.sig: PGP signature of SHA256SUMS
• owenthewizard.asc: Signing public key
• i3lockr.fish: Shell completions for fish
• i3lockr.elv: Shell completions for elvish
• i3lockr.bash: Shell completions for bash
• i3lockr: The i3lockr executable
• i3lockr.debug: The i3lockr executable, with debug info
• _i3lockr: Shell completions for zsh