Log Message:
janet: Update to 1.8.0

## 1.8.0 - 2020-03-29
- Add `reduce2`, `accumulate`, and `accumulate2`.
- Add lockfiles to `jpm` via `jpm make-lockfile` and `jpm load-lockfile`.
- Add `os/realpath` (Not supported on windows).
- Add `os/chmod`.
- Add `chr` macro.
- Allow `_` in the `match` macro to match anything without creating a binding
  or doing unification. Also change behavior of matching nil.
- Add `:range-to` and `:down-to` verbs in the `loop` macro.
- Fix `and` and `or` macros returning nil instead of false in some cases.
- Allow matching successfully against nil values in the `match` macro.
- Improve `janet_formatc` and `janet_panicf` formatters to be more like \ 
`string/format`.
  This makes it easier to make nice error messages from C.
- Add `signal`
- Add `fiber/can-resume?`
- Allow fiber functions to accept arguments that are passed in via `resume`.
- Make flychecking slightly less strict but more useful
- Correct arity for `next`
- Correct arity for `marshal`
- Add `flush` and `eflush`
- Add `prompt` and `return` on top of signal for user friendly delimited \ 
continuations.
- Fix bug in buffer/blit when using the offset-src argument.
- Fix segfault with malformed pegs.