adding support for container recipe features

The container.yaml recipe files should be agnostic to the container technology,
meaning that instead of an option like --nv specific to singularity, we have gpu: true,
and then the container technology that is loaded can add the flags appropriate for that
feature.

Signed-off-by: vsoch <[email protected]>

Author: vsoch

CHANGELOG.md

@@ -16,6 +16,7 @@ The versions coincide with releases on pip. Only major versions will be released
 ## [0.0.x](https://github.com/singularityhub/singularity-hpc/tree/master) (0.0.x)
  - adding namespaces to make module install, show, inspect easier (0.0.24)
  - added support for env section to render to bound environment file
+ - added support for container features like gpu
  - container url does not render in docs (0.0.23)
  - addition of tcl modules, removal of un-needed database (0.0.22)
  - first update of all containers, and bugfix to pull (0.0.21)