Shen 21 updates

[tizoc]

Small changes for #10. Incomplete because I'm still unsure about what to do with exit.

• Get rid of it
• Move it to another namespace?
• Other

@rkoeninger what do you think?

[tizoc]

There is also *argv* but I wouldn't touch that one (I didn't in Shen/Scheme) since it doesn't really cause any problem (exit in particular conflicts with a function of the same name in provedit!)

[rkoeninger]

@tizoc We could just call it quit instead, although I typically put non-standard functions in a port-specific namespace, which would make it shen-cl.quit.

shen.* for kernel functions shen-cl.*, shen-sharp.*, etc. for port functions lisp.*, js.*, clr.*, etc. for underlying platform functions

[tizoc]

@rkoeninger sounds good to me, shen-cl. prefix is it.

[tizoc]

@rkoeninger I named it shen-cl.exit instead of shen-cl.quit but only because exit is the usual name for such function in most (all I know) languages, but I have no strong feelings about the naming of this function either way, I can change it if you think quit is better than exit.

[rkoeninger]

@tizoc Is there anything else you want to get in this PR or is it good to go?

[tizoc]

@rkoeninger unless you have spotted any mistake or anything I have missed, it is good to go.