[FEAT] Site: blockuser's expiry supports datetime and False
[FEAT] Site: blockuser's expiry supports datetime and False

As it already support timestamps the addition of normal datetimes is not
that far fetched. It also supports 'False' as an alias for 'never' so
scripts are independent of the API and only pywikibot needs to use the
actual API value.

This also adds the documentation for this function.

Change-Id: I352d155cea0d251f35d27e887bbc84e6ee83d549

darthbhyrava/pywikibot-local,TridevGuha/pywikibot-core,Darkdadaah/pywikibot-core,h4ck3rm1k3/pywikibot-core,Darkdadaah/pywikibot-core,hasteur/g13bot_tools_new,trishnaguha/pywikibot-core,wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core,wikimedia/pywikibot-core,VcamX/pywikibot-core,xZise/pywikibot-core,magul/pywikibot-core,npdoty/pywikibot,npdoty/pywikibot,jayvdb/pywikibot-core,valhallasw/pywikibot-core,icyflame/batman,magul/pywikibot-core,hasteur/g13bot_tools_new,happy5214/pywikibot-core,h4ck3rm1k3/pywikibot-core,jayvdb/pywikibot-core,emijrp/pywikibot-core,happy5214/pywikibot-core,smalyshev/pywikibot-core,hasteur/g13bot_tools_new