Export regex struct instead of module

Users should not have access to the module directly. Instead, export the RE
struct, and also allow users to construct regex with `RE(str)`.

src/Automa.jl

@@ -43,8 +43,7 @@ if !isdefined(Base, :get_extension)
     include("../ext/AutomaStream.jl")
 end
 
-const RE = Automa.RegExp
-using .RegExp: @re_str, opt, rep, rep1, onenter!, onexit!, onall!, onfinal!, precond!
+using .RegExp: RE, @re_str, opt, rep, rep1, onenter!, onexit!, onall!, onfinal!, precond!
 
 # This list of exports lists the API
 export RE,

src/re.jl

@@ -22,6 +22,8 @@ function RE(head::Symbol, args::Vector)
     return RE(head, args, nothing, nothing)
 end
 
+RE(s::AbstractString) = parse(s)
+
 function actions!(re::RE)
     if isnothing(re.actions)
         re.actions = Dict{Symbol, Vector{Symbol}}()
@@ -129,7 +131,8 @@ end
 const METACHAR = raw".*+?()[]\|-^"
 
 # Parse a regular expression string using the shunting-yard algorithm.
-function parse(str::String)
+function parse(str_::AbstractString)
+    str = String(str_)
     # stacks
     operands = RE[]
     operators = Symbol[]

test/runtests.jl

@@ -286,7 +286,7 @@ end
     @test Automa.generate_exec_code(ctx, machine, :debug) isa Any
 end
 
-@testset "Invalid RE.actions keys" begin
+@testset "Invalid actions keys" begin
     @test_throws Exception let
         a = re"abc"
         Automa.RegExp.actions!(a)[:badkey] = [:foo]