Use @compat for new Dict syntax

This version works on my tests with Julia 0.3.3 and with Julia 0.4.0-dev.  There are still warnings generated in version 0.4.0-dev by the line
```jl
              options = eval(parse("{" * optionstring * "}"))
```
in `src/readers.jl`  I think the best approach will be to split optionstring on ',' then split each chunk on "=>" and insert each option into the options dictionary.