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/runtests.sh

@@ -0,0 +1,46 @@
+#/bin/bash
+
+REPO_TOP=$(git rev-parse --show-toplevel)
+cd "${REPO_TOP}"
+
+echo "Basic environment"
+echo "-----------------"
+vim -Nu <(cat <<EOF
+filetype off
+set rtp+=~/.vim/bundle/vader.vim
+set rtp+=./
+filetype plugin indent on
+syntax enable
+EOF
+) +Vader! tests/*.vader && echo Success || exit 1
+
+# Run through variations of user preferences that might mess with us.
+echo
+echo "Ignore case enabled"
+echo "-------------------"
+vim -Nu <(cat <<EOF
+filetype off
+set rtp+=~/.vim/bundle/vader.vim
+set rtp+=./
+filetype plugin indent on
+syntax enable
+set ignorecase
+EOF
+) +Vader! tests/*.vader && echo Success || exit 1
+
+echo
+echo "no hyphen in iskeyword"
+echo "----------------------"
+vim -Nu <(cat <<EOF
+filetype off
+set rtp+=~/.vim/bundle/vader.vim
+set rtp+=./
+filetype plugin indent on
+syntax enable
+set iskeyword+=-
+EOF
+) +Vader! tests/*.vader && echo Success || exit 1
+
+echo
+echo "All tests are passing."
+echo