docs: " " is not allowed in html anchors
docs: " " is not allowed in html anchors

asciidoc footnotes become html anchors, and the " " character is not
allowed.

Problem identified by http://validator.w3.org.

bmwiedemann/linuxcnc-mirror,araisrobo/machinekit,Cid427/machinekit,EqAfrica/machinekit,Cid427/machinekit,kinsamanka/machinekit,Cid427/machinekit,ArcEye/MK-Qt5,ianmcmahon/linuxcnc-mirror,mhaberler/machinekit,unseenlaser/machinekit,bobvanderlinden/machinekit,strahlex/machinekit,ArcEye/machinekit-testing,ArcEye/MK-Qt5,RunningLight/machinekit,cdsteinkuehler/linuxcnc,strahlex/machinekit,bobvanderlinden/machinekit,araisrobo/machinekit,aschiffler/linuxcnc,ikcalB/linuxcnc-mirror,cdsteinkuehler/linuxcnc,araisrobo/machinekit,EqAfrica/machinekit,ikcalB/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,ikcalB/linuxcnc-mirror,bobvanderlinden/machinekit,ianmcmahon/linuxcnc-mirror,ikcalB/linuxcnc-mirror,ArcEye/MK-Qt5,narogon/linuxcnc,ianmcmahon/linuxcnc-mirror,mhaberler/machinekit,bmwiedemann/linuxcnc-mirror,RunningLight/machinekit,RunningLight/machinekit,ArcEye/MK-Qt5,kinsamanka/machinekit,unseenlaser/machinekit,araisrobo/machinekit,cdsteinkuehler/linuxcnc,Cid427/machinekit,unseenlaser/machinekit,cdsteinkuehler/linuxcnc,ianmcmahon/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,ArcEye/MK-Qt5,RunningLight/machinekit,jaguarcat79/ILC-with-LinuxCNC,Cid427/machinekit,bobvanderlinden/machinekit,kinsamanka/machinekit,aschiffler/linuxcnc,cdsteinkuehler/MachineKit,mhaberler/machinekit,araisrobo/machinekit,araisrobo/machinekit,jaguarcat79/ILC-with-LinuxCNC,RunningLight/machinekit,strahlex/machinekit,cdsteinkuehler/MachineKit,ArcEye/machinekit-testing,unseenlaser/linuxcnc,unseenlaser/machinekit,narogon/linuxcnc,unseenlaser/linuxcnc,araisrobo/machinekit,ArcEye/MK-Qt5,strahlex/machinekit,kinsamanka/machinekit,bmwiedemann/linuxcnc-mirror,ianmcmahon/linuxcnc-mirror,ArcEye/machinekit-testing,aschiffler/linuxcnc,kinsamanka/machinekit,ArcEye/machinekit-testing,aschiffler/linuxcnc,EqAfrica/machinekit,EqAfrica/machinekit,bobvanderlinden/machinekit,EqAfrica/machinekit,RunningLight/machinekit,narogon/linuxcnc,ianmcmahon/linuxcnc-mirror,unseenlaser/machinekit,ianmcmahon/linuxcnc-mirror,cdsteinkuehler/linuxcnc,bobvanderlinden/machinekit,cdsteinkuehler/MachineKit,EqAfrica/machinekit,jaguarcat79/ILC-with-LinuxCNC,EqAfrica/machinekit,ikcalB/linuxcnc-mirror,RunningLight/machinekit,cdsteinkuehler/MachineKit,kinsamanka/machinekit,Cid427/machinekit,mhaberler/machinekit,Cid427/machinekit,strahlex/machinekit,strahlex/machinekit,strahlex/machinekit,kinsamanka/machinekit,unseenlaser/linuxcnc,aschiffler/linuxcnc,ArcEye/MK-Qt5,cdsteinkuehler/linuxcnc,mhaberler/machinekit,ArcEye/MK-Qt5,jaguarcat79/ILC-with-LinuxCNC,unseenlaser/machinekit,ArcEye/machinekit-testing,ikcalB/linuxcnc-mirror,cdsteinkuehler/MachineKit,unseenlaser/linuxcnc,Cid427/machinekit,unseenlaser/machinekit,bobvanderlinden/machinekit,ArcEye/machinekit-testing,mhaberler/machinekit,ArcEye/machinekit-testing,bobvanderlinden/machinekit,narogon/linuxcnc,EqAfrica/machinekit,araisrobo/machinekit,unseenlaser/linuxcnc,bmwiedemann/linuxcnc-mirror,jaguarcat79/ILC-with-LinuxCNC,cdsteinkuehler/MachineKit,unseenlaser/machinekit,kinsamanka/machinekit,mhaberler/machinekit,ikcalB/linuxcnc-mirror,ArcEye/machinekit-testing,araisrobo/machinekit,mhaberler/machinekit,bmwiedemann/linuxcnc-mirror,narogon/linuxcnc,RunningLight/machinekit