The following changes were made to the SML/NJ Library, in addition to
deriving the `.mlb` files from the `.cm` files:

* `Compat/either` (added): Implements `signature EITHER` and `structure Either: EITHER` (see https://github.com/SMLFamily/BasisLibrary/wiki/2015-002-Addition-of-Either-module); used by RegExp Library.
* `Compat/fn` (added): Implements `signature FN` and `structure Fn: FN` (see https://github.com/SMLFamily/BasisLibrary/wiki/2015-005-Addition-of-Fn-module); used by JSON Library.
* `Compat/mono-buffer` (added): Implements `signature MONO_BUFFER` and `structure CharBuffer: MONO_BUFFER` (see https://github.com/SMLFamily/BasisLibrary/wiki/2018-001-Addition-of-monomorphic-buffers); used by JSON and PP Libraries.
* `Compat/mono-sequence` (added): Implements `signature MONO_{ARRAY,VECTOR}{,_SLICE}_EXT` and `structure Word8Slice: MONO_VECTOR_SLICE_EXT` (see https://github.com/SMLFamily/BasisLibrary/wiki/2015-003-Additional-operations-on-sequences and
https://github.com/SMLFamily/BasisLibrary/wiki/2018-001-Addition-of-monomorphic-buffers); used by SML/NJ Library.
* `HTML4/pp-init.sml` (added): Implements `structure PrettyPrint` using the SML/NJ PP Library.  This implementation is taken from the SML/NJ compiler source, since the SML/NJ HTML4 Library used the `structure PrettyPrint` provided by the SML/NJ compiler itself.
* `JSON/json-stream-parser.sml` and `JSON/json-parser.sml` (modified): Rewrote use of `Unsafe.CharVector.create` and `Unsafe.CharVector.update`; MLton assumes that vectors are immutable.
* `Util/base64.sml` (modified): Rewrote use of `Unsafe.CharVector.create` and `Unsafe.CharVector.update`; MLton assumes that vectors are immutable.
* `Util/dynamic-array.sml` (modified): Rewrote use of `Array.fromVector`.
* `Util/engine.mlton.sml` (added, not exported): Implements `structure Engine`, providing time-limited, resumable computations using <:MLtonThread:>, <:MLtonSignal:>, and <:MLtonItimer:>.
* `Util/graph-scc-fn.sml` (modified): Rewrote use of `where` structure specification.
* `Util/time-limit.mlb` (added): Exports `structure TimeLimit`, which is _not_ exported by `smlnj-lib.mlb`.  Since MLton is very conservative in the presence of threads and signals, program performance may be adversely affected by unnecessarily including `structure TimeLimit`.
* `Util/time-limit.mlton.sml` (added): Implements `structure TimeLimit` using `structure Engine`.  The SML/NJ implementation of `structure TimeLimit` uses SML/NJ's first-class continuations, signals, and interval timer.
* `Util/utf8.sml` (modified): Rewrote use of `String.implodeRev` (see https://github.com/SMLFamily/BasisLibrary/wiki/2015-003d-STRING).
