CovTools 0.5.4

Corrected CRAN errors.

CovTools 0.5.3

Fix an error in CovEst.2010OAS.

CovTools 0.5.2

Function list is moved to README file.
Following functions are added - CovEst.2003LW, CovEst.2010OAS, CovEst.2010RBLW.

CovTools 0.5.1

Functions for hypothesis tests are separated for clarity.
Initialize the following documentation:
- NEWS for keeping record of updates.
- README to briefly introduce the method.