Fix examples that break in 5df0114

Some examples break because it use inline math. This have been
fixed using the `MATHOVERWRITE` and `ONLYDISPLAY` options.
Add meta charset in demos
Improve basic interaction

* Now a right click will ask for replace symbol and the double left
  click will bublle for symbols.
* Add function to replace InvisibleTimes.
* Add setDblclick when need.
* Fix bug in replaceMiByMn due unicode number.
* Fix bug in miDblclick due the return code.
* Fix bug in opPlusMiMi since setDblclick are missing.
* Add interaction for `-`.
* Add interaction for `*`.
* Add interaction for `/`.
* Add interaction for mfrac.
* Add interaction for mroot.
* Add interaction for msqrt.
* Update documentation.
* Add demos.
* Clean up the code.