Update documentation in HOL4 examples

[jhlchan]

The examples/algebra library has changed, so the README file is amended.
A paper based on examples/fermat/twosq library is just published, so a reference is added to the README file.

[mn200]

You have included automatically generated (but now stale) files under tools/vim and the file tools/hol-mode.el.

[jhlchan]

I didn't realize that, thanks for pointing them out.

[mn200]

You shouldn't git-ignore vim/ ; that causes real files in tools/editor-modes/vim to get ignored.

[mn200]

I'm afraid your use of a slash in the middle of an ignore pattern (see output of git help ignore) will not cause old files in tools/vim to be ignored. Given that no-one will ever see these files if they make a fresh checkout, I think it might be cleanest to just not edit .gitignore at all. The effect you're after would be achieved by using the lines

**/vim/file1
**/vim/file2
etc

If you did this, you could then replace the existing .gitignore lines that capture the ignores that are actually present.

[jhlchan]

I shall leave the modification of .gitignore at your discretion.

[mn200]

Thanks for taking the time over this!