Update to 1.0.1

Upstream changes:
Changes in Rcpp version 1.0.1 (2019-03-17)

    Changes in Rcpp API:

        Subsetting is no longer limited by an integer range (William Nolan in #920 fixing #919).

        Error messages from subsetting are now more informative (Qiang and Dirk).

        Shelter increases count only on non-null objects (Dirk in #940 as suggested by Stepan Sindelar in #935).

        AttributeProxy::set() and a few related setters get Shiled<> to ensure rchk is happy (Romain in #947) fixing #946).

    Changes in Rcpp Attributes:

        A new plugin was added for C++20 (Dirk in #927)

        Fixed an issue where 'stale' symbols could become registered in RcppExports.cpp, leading to linker errors and other related issues (Kevin in #939 fixing #733 and #934).

        The wrapper macro gets an UNPROTECT to ensure rchk is happy (Romain in #949) fixing #948).

    Changes in Rcpp Documentation:

        Three small corrections were added in the 'Rcpp Quickref' vignette (Zhuoer Dong in #933 fixing #932).

        The Rcpp-modules vignette now has documentation for .factory (Ralf Stubner in #938 fixing #937).

    Changes in Rcpp Deployment:

        Travis CI again reports to CodeCov.io (Dirk and Ralf Stubner in #942 fixing #941).

(wen)