Add a feature to open libfontconfig at runtime.

The feature is "fontconfig-dlopen".

This potentially makes installation with plotting simpler, because
exotic setups might not have libfontconfig in a "normal" place, and
finding the relevant pkg-config can be a headache, etc. etc.

As there's a good many features now available, these have now been
spaced out and commented.

Cargo.toml

@@ -25,31 +25,47 @@ opt-level = 2
 
 [features]
 default = ["plotting"]
+
 # Use CUDA code with double-precision floats.
 cuda = [
     "mwa_hyperdrive_cuda",
     "mwa_hyperdrive_beam/cuda",
     "mwa_hyperdrive_srclist/cuda",
 ]
+
 # Use CUDA code with single-precision floats.
 cuda-single = [
     "cuda",
     "mwa_hyperdrive_cuda/cuda-single",
     "mwa_hyperdrive_beam/cuda-single",
     "mwa_hyperdrive_srclist/cuda-single",
 ]
+
 # Enable plotting.
 plotting = ["plotters"]
+
+# Use dlopen to find libfontconfig at runtime.
+fontconfig-dlopen = ["plotters/fontconfig-dlopen"]
+
+# Compile cfitsio statically and link it
 cfitsio-static = [
     "mwa_hyperdrive_common/cfitsio-static",
     "birli/cfitsio-static",
 ]
+
+# Compile cfitsio statically and link it
 erfa-static = ["mwa_hyperdrive_common/erfa-static", "birli/erfa-static"]
+
+# Compile HDF5 statically and link it
 hdf5-static = [
     "mwa_hyperdrive_beam/hdf5-static",
     "mwa_hyperdrive_srclist/hdf5-static",
 ]
+
+# Link CUDA statically
 cuda-static = ["mwa_hyperdrive_common/cuda-static"]
+
+# Link all C dependencies statically
 all-static = ["erfa-static", "hdf5-static", "cfitsio-static", "cuda-static"]
 
 [dependencies]

mdbook/src/installation/from_source.md

@@ -39,6 +39,9 @@
 - Version must be `>=2.11.1`
 - Arch: `pkg-config` `make` `cmake` `freetype2`
 - Ubuntu: `libfreetype-dev` `libexpat1-dev`
+- Installation may be eased by using the `fontconfig-dlopen` feature. This means
+  that `libfontconfig` is used at runtime, and not found and linked at link
+  time.
 ```
 
 ```admonish tip title="CUDA (for accelerated sky modelling)"