harec uses environment variables to find typedef files for modules referenced in
the current unit (including transitive dependencies). The user is responsible
for building dependencies first and ensuring that they appear in the
environment. The variable HARE_TD_$MOD should contain the path where harec can
find the typedef file for the module $MOD. For example, if
HARE_TD_encoding::utf8 contains the value "/tmp/encoding_utf8.td", harec would
expect /tmp/encoding_utf8.td to contain encoding::utf8's typedefs. If a module
is referenced without the associated environment variable being present, harec
will error out.

In addition, harec also recognizes the following environment variables:
- NO_COLOR: Disables color output when set to a non-empty string.
- HAREC_COLOR: Disables color output when set to 0, enables it when set to any
  other value. This overrides NO_COLOR.