Make complementSumstats.R write file output by default

[espenhgn]

Fixes #157

Changes proposed in this pull request:

• Made complementSumstats.R script write output to file by default.
• The default chromosome # output column is CHR (renamed from #CHROM)
• Added test of rename_column function in fun.R script.

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[deepchocolate]

Great! I've added a fix for one of the test scripts that fails due to `nargs=Inf in #160 .

If you wish, you could add a unittest of rename_columns() in this script:
https://github.com/comorment/containers/blob/f7329b8c38a74194b65d4da23b7e53360e221a5a/usecases/LDpred2_test/unittest/fun.R

But it works as is!