This package depends on CRAN 'redux', which requires the 'hiredis'
system library. Installing on a system without hiredis leads to

```
------------------------- ANTICONF ERROR ---------------------------
Configuration failed because hiredis was not found. Try installing:
 * deb: libhiredis-dev (Debian, Ubuntu, etc)
 * rpm: hiredis-devel (Fedora, EPEL)
 * brew: hiredis (OSX)
If hiredis is already installed, check that 'pkg-config' is in your
PATH and PKG_CONFIG_PATH contains a hiredis.pc file. If pkg-config
is unavailable you can set INCLUDE_DIR and LIB_DIR manually via:
R CMD INSTALL --configure-vars='INCLUDE_DIR=... LIB_DIR=...'
--------------------------------------------------------------------
```