#116 replace move with std::move to fix R CMD check warning on recent…

… versions of clang compilers

reduction of timings of the examples of document_term_matrix, documen…

…t_term_frequencies, document_term_frequencies_statistics, cooccurrence, dtm_bind, keywords_collocation

fix r cmd check warning on use of bitwise &

news as on cran

use html_vignette to reduce package size

docusaurus

example conditional on availability of topicmodels

docusaurus

document_term_matrix gains extra argument

Fix for #49 - CRAN requirement: Packages which use Internet resources…

… should fail gracefully with an informative message if the resource is not available (and not give a check warning nor error).