Add findall regex support for InlineStrings

[bkamins]

Now we have:

julia> findall(r".", InlineString("123"))
ERROR: ArgumentError: regex search is only available for the String type; use String(s) to convert
Stacktrace:
 [1] findnext(r::Regex, s::String3, idx::Int64)
   @ Base .\regex.jl:418
 [2] findall(t::Regex, s::String3; overlap::Bool)
   @ Base .\regex.jl:462
 [3] findall(t::Regex, s::String3)
   @ Base .\regex.jl:459
 [4] top-level scope
   @ REPL[70]:1

[quinnj]

Thanks for the report; PR up: #30