Add `cmd/genop` program to generate operator functions in `interp/op.go`.
For each operator, determine its type, handle argument types conversion if necessary.
Arithmetic operators are added for now. Assign and comparison operators coming in a next commit.
* style: fix warnings from golangci-lint printed by `make check`
* style: err assign in if block when possible. Better use of switch/case
* style: err assign in if block when possible
* ast: improve error handling
* ast: handle select
* dyngo: set filename of executed script
* cfg: improve error reporting
* Implement select for receiving channels
* feat(select): add support for sending channels in case clauses
* test: improve tests on select
* feat(select): add support for "default" case
This fixes problems due to storing binary symbols as interfaces{}
instead of concrete type, which confuses lookup functions to retrieve
methods etc. in reflect.
