Consider storing stat results in a struct

[jakewilliami]

Consider storing stat results in a struct rather than indexing the st_flags attribute directly.

Something like this (untested):

struct BSDStatStruct
    st_dev::UInt64
    st_mode::UInt64
    st_nlink::UInt64
    st_uid::UInt64
    st_gid::UInt64
    st_rdev::UInt64
    st_ino::UInt64
    st_size::UInt64
    st_blksize::UInt64
    st_blocks::UInt64
    st_flags::UInt64
    st_gen::UInt64
    st_atime::Int
    st_mtim::Int
    st_ctim::Int
    st_birthtim::Int
end

function _st_flags(f::AbstractString)
    stat_t = Ref{BSDStatStruct}()
    ccall(:jl_lstat, Cvoid, (Cstring, Ref{BSDStatStruct}), f, stat_t)
    return stat_t.x.st_flags
end

[jakewilliami]

Should also consider the same for statfs results. See #20.