[hist] Add tutorial for weighted filling

[hahnjo]

No description provided.

[hahnjo]

Tutorial output:

hist1 with expected mean = 10
entries = 25000, mean = 9.99652, stddev = 4.99767
 |                                        |
 |                                        |
 |                                        |
 |                                        |
 |                                        |
 |                   *                    |
 |                ********                |
 |              ************              |
 |           *****************            |
 |          ********************          |
*|        ************************        |*
*|      ***************************       |*
*|    ********************************    |*
*|   ***********************************  |*
*|****************************************|*

hist2 with distorted normal distribution
entries = 25000, mean = 13.2862, stddev = 4.69151
 |                                        |*
 |                                        |*
 |                          *             |*
 |                      *******           |*
 |                     **********         |*
 |                    **************      |*
 |                   ***************      |*
 |                  *****************     |*
 |                ********************    |*
 |               ************************ |*
 |              **************************|*
 |             ***************************|*
 |           *****************************|*
 |         *******************************|*
*|      **********************************|*

bin errors of hist3 (not to scale)
 |                                        |*
 |                                        |*
 |                                        |*
 |                                        |*
 |                                        |*
 |                              * *       |*
 |                         ************ * |*
 |                        *************** |*
 |                     *******************|*
 |                   *********************|*
 |                 ***********************|*
 |                ************************|*
 |             ***************************|*
 |          ******************************|*
*|      **********************************|*

[github-actions]

Test Results

    21 files      21 suites   3d 15h 17m 25s ⏱️
 3 691 tests  3 690 ✅ 0 💤 1 ❌
75 646 runs  75 645 ✅ 0 💤 1 ❌

For more details on these failures, see this check.

Results for commit e01ec94.

♻️ This comment has been updated with latest results.

[hageboeck]

Let's add the output to the doxygen-generated page?
Example

Suggested change

	/// \macro_code
	/// \macro_code
	/// \macro_output

[hageboeck]

Suggested change

	// It is currently not possible to directly draw RHist's, so this function implements an output with ASCII characters.
	// It is currently not possible to directly draw RHist, so this function implements an output with ASCII characters.

[hageboeck]

Should we show the types?

Suggested change

	ROOT::Experimental::RRegularAxis axis(40, {0, 20});
	ROOT::Experimental::RRegularAxis axis(40, {0., 20.});

[hageboeck]

Many users will understand immediately when squared weights are mentioned:

Suggested change

	// Create and fill a third histogram with the special RBinWithError bin content type.
	// Create and fill a third histogram with the special RBinWithError bin content type.
	// This tracks both the sum of weights and the sum of squared weights.

[hageboeck]

Maybe this could be renamed? See (see screenshot below):

Suggested change

	\defgroup tutorial_histv7 RHist tutorials