Self-defined error type

Add self-defined error type in the crate

v0.1.3

Fix bug in export verilog

Fix bug in verilog-parser

Fix bug in verilog parser. Before this release, the verilog-parser parses from *.v, there will remain extra whitespace in identifier(net name, gate name). Fixed

Initial release

Initial release feature

1. generic data structure.
2. support Verilog import/export