Add part of baselib functions only #255

• GopherLua is a Lua5.1 implementation. You should be familiar with Lua programming language. Have you read Lua 5.1 reference manual carefully?
• GopherLua is a Lua5.1 implementation. In Lua, to keep it simple, it is more important to remove functionalities rather than to add functionalities unlike other languages . If you are going to introduce some new cool functionalities into the GopherLua code base and the functionalities can be implemented by existing APIs, It should be implemented as a library.

Please answer the following before submitting your issue:

1. What version of GopherLua are you using? : 1cd887c
2. What version of Go are you using? : 1.13
3. What operating system and processor architecture are you using? : linux/amd64
4. What did you do? : N/A
5. What did you expect to see? : N/A
6. What did you see instead? : N/A

I want to add part of the baselib functions to LState, but there is no way to do that since every baselib function implementation is private.
What about add something like OpenBaseStrip which can pass a list of baselib function name, and add them to LState.