Various optimizations, Readme update, Bench script for imports

examples/import_bench.jl

@@ -0,0 +1,28 @@
+using metagraph_optimization
+using BenchmarkTools
+using Base
+using Base.Filesystem
+
+function bench_txt(filepath::String)
+    name = basename(filepath)
+    name, _ = splitext(name)
+
+    println(name, ":")
+    g = import_txt(filepath)
+    print(g)
+    println("  Graph size in memory: ", bytes_to_human_readable(Base.summarysize(g)))
+    @btime import_txt($filepath)
+    println()
+end
+
+function main()
+    bench_txt("examples/AB->AB.txt")
+    bench_txt("examples/AB->ABBB.txt")
+    bench_txt("examples/AB->ABBBBB.txt")
+    bench_txt("examples/AB->ABBBBBBB.txt")
+    #bench_txt("examples/AB->ABBBBBBBBB.txt")
+    bench_txt("examples/ABAB->ABAB.txt")
+    bench_txt("examples/ABAB->ABC.txt")
+end
+
+main()