Changes

Computer Modern and Latin Modern use the msbm font family for black board [[Blackboard bold|blackboard bold]]. msbm look very dull and usually black board bold should be avoided in math. However, there are certain cases where one needs something ''fancier'' than math bold. The [http://ctan.org/tex-archive/fonts/doublestroke doublestroke fonts] offer one such alternative. This is how these can be used with ConTeXt. Note that since we are using doublestroke fonts as the blackboard font, there is really no need to use the blackboard fonts separately. So, the mb math family is reused.