A buildpack for including the ICU library into a Heroku dyno. This is required as a dependency for several tools.

This buildpack makes ICU4C available in the /app/icu directory for both compilation and runtime uses. The primary purpose of this is to allow Charlock Holmes (a Ruby gem for encoding heuristics) to run on Heroku.

In order to achieve this, the following happens:

1. ICU is downloaded and compiled from source
2. The compiled library is cached for future builds
3. The compiled result is copied into /app/icu and $1/icu (the build directory) to make it available in a seemingly consistent location during both compilation and runtime
4. A Bundler config option is exported to the rest of the compilation process to ensure Charlock Holmes looks for ICU in the correct place.