The 1965-1966 Broadway season is creeping into the wings. It had many qualities, good and bad, but possibly one of the only reasons it can enter the ""memorable"" category is that it is the first season to have a diary. And this is it. Mr. Gaver, UPI drama critic has chronicled incidents and incidentals, probed backstage at productions and views the scene with the air of a bemused but benign father. It is enlightening. Would you like to know just what Samuel French, Inc. is really like? Would you appreciate an ""extra"" on the Peter Bull vs. David ""Merrickana"" debate or enjoy recalling Stanley Kauffmann's ""preview"" experience? Would you be interested in one of Charenton's inmates reaction to her play-- loathe and detest everything about about the production. We all loathe it. We're dying for the end to come so we'll never ever have to do it again."" Then there's the fact that Gwen Verdon's a grandmother, that Generation cost $78,258.84, that You Can't Take It With You almost never made its Broadway debut and that Ian Richardson's derriere-area inspired some erotic fan mail. . Unfortunately, many of the niceties recorded here may be lost on all but the most avid theatrical follower. But then there are always those people who read other people's diaries. The first of a series of Seasons.