Increment version number to 5.1.0

CRAN submission 5.0.1

Merge pull request #528 from massimoaria/develop

Bibliometri 5.0.0 - Cran Submission

Merge pull request #477 from massimoaria/develop

CRAN submission 4.3.0

Merge pull request #454 from massimoaria/develop

Develop

Merge pull request #407 from massimoaria/develop

CRAN Release 4.1.4

Merge pull request #359 from massimoaria/develop

Minor fix

Merge pull request #304 from massimoaria/develop

Merge pull request #303 from massimoaria/master

Merge pull request #287 from massimoaria/develop

Develop to CRAN

Minor fix