Support Symbol column parser

[yakir12]

This is from using JuliaDB:

using DelimitedFiles, JuliaDB
x = [[:x, :a, :b, :c] [:y, 1, 2, 3]]
writedlm("tmp.csv", x)
t = loadtable("tmp.csv", colparsers = [Symbol, Int], delim='\t') # ERROR: MethodError: no method matching 
fromtype(::Type{Symbol})

[davidanthoff]

I assume the only real problem here is to support Symbol, the float case should work, right? In particular, if you said colparsers = [String, Float64], everything should work?

[yakir12]

Yes, you are correct. I realize my specific example was a bit misleading (what with the Int and Float64), so I made it clearer (and corrected a mistake with the delimiter).