requesting a list via config.get has issues with environment variables

[wryfi]

There is currently no bug-free way to specify a single-element list as an environment variable.

Setting the environment variable to a string, and explicitly asking the config manager for a list, produces this:

> export TEST__FOO__ALIST=abc
> export TEST__FOO__BLIST=abc,def
> ipython
...
In [1]: from cfitall.config import ConfigManager

In [2]: config = ConfigManager("test")

In [3]: config.get("foo.alist", list)
Out[3]: ['a', 'b', 'c']

In [4]: config.get("foo.blist", list)
Out[4]: ['abc', 'def']

Appending a comma to the environment variable returns a two-item list, with an empty second item:

> export TEST__FOO__ALIST=abc,
> ipython
...
In [1]: from cfitall.config import ConfigManager

In [2]: config = ConfigManager("test")

In [3]: config.get("foo.alist", list)
Out[3]: ['abc', '']

Please devise a better syntax that accommodates single-element lists as environment variables.