unit testing: fix symbol

check: move Symbol to a single file

CLI: fix file input

AST: redefine 'Instance'

type checker: fix missing checking of new instances

type checker: fix 'Symbol::from_instance'

type checker: add more restrict on binds & fix missing of popping stack

*: replace typename with 'Self' in impl block

CLI: improve code input (no more typing EOF)

CLI: improve code

CLI: replace clap with structopt

CLI: add function 'interactive_loop'

CLI: add function 'analysis_file'

for all: format code via 'cargo fmt'

example: rename '.preprocess.ichigo' -> '.ascii.ichigo'