core: fix search/insert of elements in sorted arraylist with duplicates

The pointer and index returned is now the first element found with the value
(with the lower index if there are many elements with same value).
And the index for insert is the last element with same value + 1
(the higher index + 1).
core: add a .mailmap file

This file is used for example by command "git shortlog", to prevent duplicate
committers.
core: fix .mailmap entries for myself
core: remove extra spaces in a comment
tests: add some tests on function eval_expression
tests: initialize argc to -1 instead of 1 before some tests
tests: add extra check of argv pointer in test of string_split functions
tests: add test of function string_split_shell with an empty string
core: move default prefix/suffix for evaluation in wee-eval.h
core: add hide of chars in string in evaluation of expressions

The syntax is: ${hide:char,string}.
All chars in string are replaced with char (which can be one or more chars).
tests: fix memory leak in hashtable tests
core: fix memory leak in completion
core: call "callback_free" in functions arraylist_{remove|clear|free}

This fixes a memory leak in completions which are using this callback
to free words in the completion list.
api: add regex replace feature in function string_eval_expression
core: display time in bare display only if option weechat.look.buffer_time_format is not an empty string