Release v0.18.0

[terrillmoore]

Update README, etc. See delta in #123 for details.

• update VERSION.txt version to v0.18.0
• update library.properties version to 0.18.0
• update CATENA_ARDUINO_PLATFORM_VERSION in CatenaBase: change here:
  

  Catena-Arduino-Platform/src/CatenaBase.h

  Line 58 in 3af42bb

  #define CATENA_ARDUINO_PLATFORM_VERSION CATENA_ARDUINO_PLATFORM_VERSION_CALC(0, 15, 0, 0) /* v0.15.0.0 */

• update README.md version for badges (line 7)
• update README.md release history (towards end).
• generate pull request
• merge into master.
• tag and release.

[terrillmoore]

The changes for input command editing and fixing the Si1133 should be generally available.