Update to 0.5.3

• Fix markup typo in the man page.
• Abort on line numbering or column numbering overflow. Line numbers are limited to values that fit in "unsigned int". Also reject input lines longer than 2^32-1 characters. It seems reasonable to presume that any input that violates these constraints is someone screwing around and not a serious attempt to compile or preprocess anything useful. Done in response to n2129, but without getting into any of the silliness found there.
• Recognize ia64 for IA64 builds.
• Recognize aarch64 for 64-bit ARM builds, as sent in by various people.
• Recognize riscv and riscv64 for risc-v builds.