Fix for <Leader>x and other minor issues

Fixed a bug in <Leader>x (todo#PrependDate) introduced last commit.
Fixed case sensitivity bug in todo#ToggleMarkAsDone() and todo#UnMarkAsDone()
Fixed errors being reported for repeat#set if vim-repeat plugin is not installed.
Fixed modeline in .vim files to work (only works on first/last 5 lines of file), and made the modelines consistent across all files.
New unit tests for todo#ToggleMarkAsDone()
Minor fixes for README.md and man page
Fix anchoring of RegExp in todo#ToggleMarkAsDone
Fixed a bug in overdue highlighting that resulted in the current date being matched on round dates like the 20th and 30th.
Added more unit tests for overdue date highlighting.
Corrected RegExp anchoring on today date highlighting.
Added a few bash scripts to make running unit tests easier and more reliable, including testing with ignorecase user preference set.

tests/todo.vader

@@ -3,7 +3,6 @@
 " Author:      Peter (fretep) <githib.5678@9ox.net>
 " Licence:     Vim licence
 " Website:     http://github.com/dbeniamine/todo.txt.vim
-" vim: ts=2 sw=2 sts=2 expandtab :help tw=78 cc=80 foldmethod=marker
 
 " [Vader](https://github.com/junegunn/vader.vim) is a simple unit testing
 " plugin for VIM.
@@ -416,8 +415,74 @@ Execute (16-12-31 should NOT match with reference 17-12-31):
 Execute (2016-12-31 should NOT match with reference 17-12-31):
   Assert '2016-12-31' !~ b:rex
 
+" Make sure current date doesn't match
+Before:
+  let b:rex = todo#GetDateRegexForPastDates(strftime("%Y"), strftime("%m"), strftime("%d"))
+Execute (Log generated RegExp):
+  Log b:rex
+Execute (Current date should not match):
+  Assert strftime("%Y-%m-%d") !~ b:rex
+
+" Incorrectly matching current date, some breakpoints that previously were found to be an issue
+Before:
+  let b:rex = todo#GetDateRegexForPastDates(2017,09,20)
+Execute (Log generated RegExp):
+  Log b:rex
+Execute (2017-09-19 should match with reference 2017-09-20):
+  Assert '2017-09-19' =~ b:rex
+Execute (2017-09-20 should NOT match with reference 2017-09-20):
+  Assert '2017-09-20' !~ b:rex
+Before:
+  let b:rex = todo#GetDateRegexForPastDates(2017,09,30)
+Execute (Log generated RegExp):
+  Log b:rex
+Execute (2017-09-29 should match with reference 2017-09-30):
+  Assert '2017-09-29' =~ b:rex
+Execute (2017-09-30 should NOT match with reference 2017-09-30):
+  Assert '2017-09-30' !~ b:rex
+
 " file: autoload/todo.vim {{{1
 
+" function! todo#ToggleMarkAsDone(status) {{{2
+
+" NOTES:
+"   - Rules on leading whitespace is not clear, and really could be taken
+"     either way. Current behaviour is to treat leading whitespace as valid.
+"     TODO: Ensure behavior of leading whitespace is consistent for everything
+"     including priorities (which are currently not).
+"   - FIXME: Incorrect handling of priorities is expected below, see #21.
+Given todo (Tasks):
+  x 2017-09-18 Complete task
+  x 2017-09-18 2017-09-01 Completed task with a created date
+  x 2017-09-18 (A) Completed priority task
+  x 2017-09-18 2017-09-01 (A) Completed priority task with a created date
+  X 2017-09-18 Not to be confused for a complete task
+  Active task
+  2017-09-01 Active task with a created date
+  (A) Active priority task
+  (A) 2017-09-01 Active priority task with a created date
+  X 2017-09-18 Not to be confused for a complete task
+  XNot to be confused for a complete task
+   x 2017-09-18 Rules are not clear on leading whitespace, see comments in test
+  Tricky incomplete task x 2017-09-18
+Execute (Toggle completed):
+  global/./call todo#ToggleMarkAsDone('')
+  execute "%substitute/" . strftime("%Y-%m-%d") . "/**TODAY**/"
+Expect todo (Toggled tasks with today as **TODAY**):
+  Complete task
+  2017-09-01 Completed task with a created date
+  (A) Completed priority task
+  2017-09-01 (A) Completed priority task with a created date
+  x **TODAY** X 2017-09-18 Not to be confused for a complete task
+  x **TODAY** Active task
+  x **TODAY** 2017-09-01 Active task with a created date
+  x (A) **TODAY** Active priority task
+  x (A) **TODAY** 2017-09-01 Active priority task with a created date
+  x **TODAY** X 2017-09-18 Not to be confused for a complete task
+  x **TODAY** XNot to be confused for a complete task
+  Rules are not clear on leading whitespace, see comments in test
+  x **TODAY** Tricky incomplete task x 2017-09-18
+
 " function: todo#SortDue() {{{2
 
 Before:
@@ -678,3 +743,4 @@ Then (Is cursor on first non-overdue task?):
 After:
     unlet g:TodoTxtSortDueDateCursorPos
 
+" vim: tabstop=2 shiftwidth=2 softtabstop=2 expandtab foldmethod=marker