Stop special casing InlineString1

[KristofferC]

I was looking into fixing #15 but realized that the special casing of InlineString1 to only have one byte makes that not work. I would say that the current special casing of InlineString1 creates quite a bit of confusing behavior:

julia> InlineString("") |> typeof
String3

julia> InlineString("a") |> typeof
String1

Why would an empty string take more place than a one-letter string?

---

julia> String1("")
ERROR: ArgumentError: string too large (0) to convert to String1
Stacktrace:
 [1] stringtoolong(T::Type, n::Int64)
   @ InlineStrings ~/.julia/packages/InlineStrings/xUsry/src/InlineStrings.jl:321
 [2] String1(x::String)
   @ InlineStrings ~/.julia/packages/InlineStrings/xUsry/src/InlineStrings.jl:208
 [3] top-level scope
   @ REPL[4]:1

julia> String3("")
""

Wut?

---

julia> rstrip(String3("aaa")) |> typeof
String3

julia> rstrip(String1("a")) |> typeof
String3

Why would rstrip make it bigger?

---

julia> inlinestrings(["a", "b", ""])
ERROR: ArgumentError: string too large (0) to convert to String1
Stacktrace:

This looks like a bug?

---

There are also casts to InlineString3 that have to be done for many of the operations on InlineString1 which probably makes them slower than storing the two bytes.

There is nothing in the documentation that indicates this type of special behavior.

I'm sure there is some reason for doing this since so much pain seems to have been gone through to do it but I thought I would put up this PR nonetheless.

Fixes #73 Fixes #72

[quinnj]

Yeah, this is probably fine; the integration tests pass, so it doesn't look like it'd be breaking from that perspective. I say go for it.