Support tilde ~ in key file path

[slawekjaranowski]

Add suport tilde ~ in key file path.

If keyFile begin with tilde followed by / slash or \ backslash depends on os, like

~/path-to-key.asc

should be replace by

${user.home}/path-to-key.asc

In class PGPKeyInfo we need to change method keyFromFile and confirm by unit tests

[slawekjaranowski]

connected with #81

[mccartney]

I think the challenge here is that the configured paths already come as java.io.File type values.

One not-so-clean option is to unpack the File to name and create another File instance with modified file path.

[slawekjaranowski]

We can try in this way ...
magic can be done somewhere in PGPKeyInfo#keyFromFile method

Probably will be the best to do next method which is responsible for such translation and it can be easy tested by unit test

At the end we need nio..Path so we can translate from File to Path