: use new `params` in all functions that have keyword params, in order to remove their vars from the environment. note that functions that use $? (such as die()) must save it *before running params, because params will overwrite $?.

web/links/index.htm: updated to Firefox bookmarks. added bash and MySQL-related bookmarks, including MySQL doc subfolder.

lib/sh/util.sh: params(): added doc comment

lib/sh/util.sh: added params(), which removes keyword-param-only vars from the environment

lib/sh/util.sh: added unexport() (note that `declare +x` won't work because it defines the var if it isn't set)

lib/sh/util.sh: moved vars section to beginning so other sections can use it (it does not contain logging statements, so it doesn't need to be after verbose output)

bugfix: lib/sh/util.sh: command(): limit cmd_log_fd directly instead of limiting log_fd (usually fd 2) and then redirecting cmd_log_fd to it. this ensures that stderr is not limited unless it's actually used as the cmd_log_fd, so that a non-logging stderr will still reach the user properly regardless of whether err_fd is set to something other than 2. (previously, without an err_fd at 22, closing fd 2 at the beginning of the set of redirections would leave no fd pointing to a place to echo errors to.)

lib/sh/util.sh: disable_logging(): use echo_eval instead of plain eval so the disabling of logging is nevertheless itself logged

lib/sh/util.sh: command(): made usage message an end-of-line comment

lib/sh/util.sh: inlined limit_log_fd into command() since it's only used once