Update and synchronize ehtml documentation
yaws_api: Fix ehtml {check, _, number()} attributes

Attribute {check, Key, 10} should expand the same way as {Key, 10}.
yaws_api: Allow binary attribute values in ehtml

Binary attribute values are already supported in exhtml.
yaws_api: Cosmetics (reduce redundancy)
Fix building without PAM

Fixes this error in `make`:

    /usr/bin/install: cannot stat ‘epam’: No such file or directory
    make[1]: *** [post-build] Error 1
Fix typo in configure help (`--disable-pam`)
Merge pull request #184 from weisslj/fix-build-without-pam

Fix building without PAM (and small typo in configure help)
Merge pull request #183 from weisslj/ehtml-attribute-fixes

EHTML: Fix small bug, allow binary attribute values and update documentation