Benchmark names are too long

[harendra-kumar]

We should not use the whole absolute path of the corpus file in the benchmark name.

compress/files/bufsize(65536)/compress 5//home/harendra/composewell/streamly-lz4/corpora/large/bible.txt.normalized time                 41.77 ms

compress/files/bufsize(65536)/compress 5//home/harendra/composewell/streamly-lz4/corpora/large/world192.txt.normalized time                 33.97 ms

compress/files/bufsize(65536)/compress 5//home/harendra/composewell/streamly-lz4/corpora/cantrbry/alice29.txt.normalized time                 39.86 ms