merge: minor tidying

merge: minor tidying

 * clang-format
 * readme: split out contributors
 * rename fd parameters
 * increase buffer sizes to avoid truncation
 * test: add missing #include guards
 * unify char buffer inititialisation
 * boolify: locals, params, args
 * rename mailbox functions
 * light tidying
 * don't check for empty config strings
 * rename struct Event and Mailbox.notify
 * move el_free() to email
 * tidy maildir_mbox_check()
 * config: rename listener to observer
 * tidy ternary operators
 * tidy char pointers
 * initialise pointers
 * tidy pointer definitions