(f90-keywords-re, f90-keywords-level-3-re)

(f90-keywords-re, f90-keywords-level-3-re)
(f90-procedures-re, f90-operators-re, f90-hpf-keywords-re): Use regexp-opt.
(f90-keywords-re, f90-keywords-level-3-re): Add `pure' and `elemental'.
(f90-procedures-re): Add `null' and `cpu_time' from F95.
(f90-font-lock-keywords-1): Minor reorganization so we don't need
`override' any more.
(f90-font-lock-keywords-3): Use `keep' rather than `override'.
(f90-indent-subprogram): Use indent-region.
(f90-break-line): Use indent-according-to-mode.