Make Unicode escapes more consistent with recent improvements made to https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/strings

1.  Moved `\v` row up to be just under `\t`. This move provides for a more logical grouping of the escape sequences: simple, static ones first, followed by the dynamic Unicode escape sequences that require a user-supplied value. I think having this grouping will make the list more readable for most readers, which I feel is more important than maintaining strict alphabetical ordering of the list. The `\v` just seemed out of place between `\u` and `\x`, and if someone is looking for a Unicode escape sequence, I believe it helps to have those all together.

2. Switched order of `\u` and `\U` so that `\u` could come first as that, again, seems to flow better / be a more logical progression.

3. Changed character used for hex digit placeholder in escape sequence from `n` to `H`, as again, I feel it is more readable / more intuitive that "H" refers to "Hex" whereas "n" is ambiguous as "number"? And, it has more visual clarity since the lower-case "n" blends in a bit with "u" (at least to me it does).

4. Added range for all user-supplied values (why make readers hunt elsewhere for that info, especially when `\U` is not as obvious as the other two?).

5. Added generic format for `\x`

6. Change example code point / character for `\u` and `\x` to something a little more interesting than "A" :-)

7. Added missing example permutation of `\x`

For more details, please visit: https://bit.ly/UnicodeEscapeSequences