uniquify might could use gensym?

I saw this helper function [uniquify](https://github.com/AlgebraicJulia/AlgebraicRelations.jl/blob/951be8010824d307d503b5eb80c367564a22b1e5/src/SQL.jl#L12) and it looks like you are manually creating unique symbols. Julia provides a builtin for that called [gensym](https://docs.julialang.org/en/v1/base/base/#Base.gensym) which makes symbols.

```julia
julia> gensym("foo")
Symbol("##foo#253")
```

it looks like you can't use `#` in SQL identifiers, so maybe gensym and then [replace](https://docs.julialang.org/en/v1/base/strings/#Base.replace-Tuple{AbstractString,Pair}) would work like:

```julia
replace(gensym(tag), "#"=>"_")
```