Added a macro to simplify inserting site urls

i2p2www/pages/global/layout.html

i2p2www/pages/global/macros

i2p2www/pages/global/nav.html

i2p2www/pages/global/urlify

i2p2www/pages/site/docs/how/cryptography.html

i2p2www/pages/site/docs/how/elgamalaes.html

i2p2www/pages/site/docs/how/garlicrouting.html

i2p2www/pages/site/docs/how/index.html

i2p2www/pages/site/docs/how/intro.html

i2p2www/pages/site/docs/how/networkcomparisons.html

i2p2www/pages/site/docs/how/networkdatabase.html

i2p2www/pages/site/docs/how/peerselection.html

i2p2www/pages/site/docs/how/threatmodel.html

i2p2www/pages/site/docs/how/tunnelrouting.html

i2p2www/pages/site/docs/techintro.html