Add make target to run benchmarks

[llogiq]

Something like the following script:

/bin/time --format="binary_trees\t%e\t%U\t%S" bin/binary_trees 20 > /dev/null && \
/bin/time --format="fannkuch_redux\t%e\t%U\t%S" bin/fannkuch_redux 12 > /dev/null && \
/bin/time --format="fasta\t\t%e\t%U\t%S" bin/fasta 25000000 > /dev/null && \
/bin/time --format="fasta_redux\t%e\t%U\t%S" bin/fasta_redux 25000000 > /dev/null && \
/bin/time --format="k_nucleotide\t%e\t%U\t%S" bin/k_nucleotide 0 < data/k_nucleotide.txt > /dev/null && \
/bin/time --format="mandelbrot\t%e\t%U\t%S" bin/mandelbrot 16000 > /dev/null && \
/bin/time --format="n_body\t\t%e\t%U\t%S" bin/n_body 50000000 > /dev/null && \
/bin/time --format="regex_dna\t%e\t%U\t%S" bin/regex_dna 0 < data/regex_dna.txt > /dev/null && \
/bin/time --format="reverse_comp.\t%e\t%U\t%S" bin/reverse_complement 0 < data/reverse_complement.txt > /dev/null && \
/bin/time --format="spectralnorm\t%e\t%U\t%S" bin/spectralnorm 5500 > /dev/null

But I'm unsure how portable this is. Also someone should check if I got the arguments right.