Log message:
Update geography/mapcode to 2.4.0. Build with thread support.

Changes in 2.4.0

- Added scripts for Korean (Choson'gul / Hangul), Burmese, Khmer,
  Sinhalese, Thaana (Maldivan), Chinese (Zhuyin, Bopomofo), Tifinagh
  (Berber), Tamil, Amharic, Telugu, Odia, Kannada, Gujarati.
- Renamed constants to more correct terms (Malay to Malayalam, Hindi to
  Devanagari).
- Added getAlphabetsForTerritory(t), returning the most commonly used
  alphabets for territory t.
- Improved some characters for Arabic and Devanagari.
- Fixed Bengali to also support Assamese.
- Improved readability of implementation.
- Added conditional define option for unittest: NO_POSIX_THREADS. Add
  -DNO_POSIX_THREADS to your compiler command-line to not use
  pthreads.h, for example, on MSVC platforms.
- Added conditional define option library: NO_FAST_ENCODE. Add
  -DNO_FAST_ENCODE to your compiler command-line to not use the fast
  encoding (default is to use fast encoding). Using fast encoding speeds
  up de encoding by a factor of 2. For normal use, there is no reason not
  to use fast encoding.
- Added parseMapcodeString to get individual mapcode elements, like the
  territory code, the 'proper' mapcode (without the territory and
  precision extension) and the precision extension parsed from a (user)
  input string.
- Additional bug fixes.

Log message:
Import mapcode 2.3.0 as geography/mapcode.
Based on a PR by Aleksej Lebedev.

A mapcode represents a location. Every location on Earth can be
represented by a mapcode. Mapcodes were designed to be short,
easy to recognise, remember and communicate. They are precise
to a few meters, which is good enough for every-day use.