Better match list for ?Random

[frankluebeck]

• removed unnecessary index entry "random element of .."
• added a new index entry in the general documentation of
  Random which only consists of the text "Random" and so
  will be the first match when a user types ?Random
• in last mentioned section: changed wording about PseudoRandom
  and improved examples
• corrected labels and added an example in ManSection on
  Random with a random source argument

This addresses issue " Merge documentation entries for 'Random'" #116

[olexandr-konovalov]

The diffs below occur in the test of manual examples. I will fix them.

########> Diff in [ "./../../lib/random.gd", 63, 67 ]
# Input is:
Random(mysource, 1, 10^60);
# Expected output:
474943581767832038339909502952186501785153672757525589711853
# But found:
999331861769949319194941485000557997842686717712198687315183
########
########> Diff in [ "./../../lib/coll.gd", 1621, 1631 ]
# Input is:
Random([1..6]);
# Expected output:
6
# But found:
1
########
########> Diff in [ "./../../lib/coll.gd", 1621, 1631 ]
# Input is:
Random(1, 2^100);
# Expected output:
216763054510766614871671341272
# But found:
866227015645295902682304086250
########
########> Diff in [ "./../../lib/coll.gd", 1621, 1631 ]
# Input is:
g:= Group( (1,2,3) );;  Random( g );  Random( g );
# Expected output:
()
(1,3,2)
# But found:
(1,3,2)
(1,2,3)
########
########> Diff in [ "./../../lib/coll.gd", 1621, 1631 ]
# Input is:
Random(Rationals);
# Expected output:
-4
# But found:
-2
########