generate ExproniconLite

[Roger-luo]

currently I manually write if else in ExproniconLite to get rid of MLStyle/MatchCore, but this is not necessary since the generated code from @match/@switch is actually dependency free.

In principle we just need to implement a print_expr function to print Julia Expr to a file after macroexpand the MLStyle macros. (the default Julia show for Expr does not guarantee its printing can be unparsed)

[Roger-luo]

now we basically support this, a few things left to do:

1. make print_expr parsable (it seems to work, but need more test on this)
2. replace the default Julia printer with print_expr so that we can generate 1.0 compatible code (or maybe not necessary)
3. integrate the bootstrap as a command in IonCLI
4. find a way to generate the static part of active pattern

cc: @thautwarm