When executing the function `package-list-packages', the column widths are too narrow, cutting off a significant portion of the package names. 

This minor patch adds three variables that can be set by the user to adjust the width of each column within the package list. 

Changelog entry

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2020-05-04  Chris McMahan  <cmcmahan@gmail.com>

* package.el ((define-derived-mode package-menu-mode tabulated-list-mode "Package Menu"):
User can now adjust column widths of the package list by setting the values of the following:

package-name-column-width (defaults to 30 columns)
package-version-column-width (14 column)
package-status-column-width (12 columns)
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