Jan 23, 2014.  1.6 -- Map G() to factor(), not as.factor(), so as to remove unused levels which
     otherwise will mess up the computation of DOF.

Jan. 4, 2014.  1.6-1180 -- On CRAN.

Dec. 17, 2013. 1.6 -- Fixed a bug in computing F-test for IV. Added F-test in 1st stage for omitted i.v.
     Suppress F-test writing for robust and clustered errors. I can't compute it.

Dec. 06, 2013. 1.6.1163 -- On CRAN.

Nov. 29, 2013. 1.6 -- Support for G(x:f) with x matrix.
     Fixed a one-off error in df for the one-factor case.
     Several bug-fixes and memory optimization pertaining to large model matrices.
     Some of them in R.

Nov. 25, 2013. 1.6 -- Matrix::rankMatrix bug has been fixed. We can
     use the sparse method qrLINPACK as soon as a new version of Matrix is released.  Bug #5031:
     https://r-forge.r-project.org/tracker/index.php?func=detail&aid=5031&group_id=61&atid=294
     Added contrasts-argument to felm. It applies to factors outside G().
     Fixed efactory() for G(x:f) interactions.

Nov. 14, 2013. 1.6 -- Added G(x:f) syntax for estimation similar to
     x:f, i.e. interaction between a covariate and a factor. felm()
     and getfe() are ok, but efactory() does not always produce
     estimable functions.

Nov. 12, 2013. 1.5-1118 -- On CRAN. Fixed a bug which prevented bootstrapping in some cases.

Oct. 28, 2013. 1.5-1107 -- On CRAN. Version presented in R journal article.