`_` is not supported in literals after the comma

[ssoelvsten]

I tried to create a module with the following program, which I thought would work as intended after #57 / #82 ?

3.1415926535_8979323846_2643383279_5028841971_6939937510_5820974944_5923078164_0628620899_8628034825_3421170679

I tried it in utop and it seems to be supported in OCaml.

[ssoelvsten]

@AStenbaek, since you have not been added to this project as a collaborator nor have any commits on master Github does not allow me to assign this issue to you.

@aslanix , adding him as a collaborator might make some project management a bit easier since merging dev-integrity into dev and that further into master seems quite far away...

[ssoelvsten]

I forgot that even though Troupe uses floating points, the frontend does not actually accept it.

[AStenbaek]

I forgot that even though Troupe uses floating points, the frontend does not actually accept it.

That was also what I noticed when I added the support for literals.
The lexer implementation can use https://github.com/ocaml/ocaml/blob/trunk/parsing/lexer.mll for inspiration as with the integer literals.