ArithEval v0.5.0 released

[Dechcaudron]

Updating this library I coded more than a year ago, so that I 
could use it as an optional dependency of the coming up dli 
library.

It allows the runtime evaluation of simple math expressions like 
`1 + 2 * 3` or `1 ^ foo`, with foo being given values at run time.

It was never announced in this forum, so it is likely most of you 
never heard of it. The README pretty much sums up all there is to 
see, but do let me know if you guys have any specific doubt. 
Feedback is greatly appreciated.