Dr Markus Kuhn published in 1999 an article [1] explaining in details
why we shouldn't use the ASCII grave accent (0x60) as a left quotation.
Backticks have been used most notably to produce nice-looking LaTeX
documents but it doesn't seem to be an issue on modern platforms and
for the oldest ones, there are workarounds as mentioned by Dr Kuhn.
[1]: https://www.cl.cam.ac.uk/~mgk25/ucs/quotes.html
Solves #2355.
In test drivers:
* Uses `mrb_t_pass_result` to check and pass test result to main `mrb_state`.
* Adds `mrb_init_test_driver` to init test `mrb_state`.
src/hash.c:
- mrb_hash_(aget|aset|dup|delete): internal linkage
- remove documentation of methods which are not implemented (in here)
- remove #assoc; unused, not in ISO spec
- remove #rassoc: same, implementation is also wrong
hash-ext mrbgem:
- remove header "mruby/khash.h"
- remove mrb_hash_values_at (move code into hash_values_at, i: long -> int)
- less whitespace in gem_init function
- reduce compile time by a little bit (full-core: ~0.7s for me)
- thanks to 'include-what-you-use' for some help
- include Standard C header files before any other (coding style)
Jun Hiroe