- Moved to file_system/ directory for consistency.

Signed-off-by: Meng Lu <lumeng.dev@gmail.com>
* Quit the script at the first failcure "set -e";
* Test existence of dependency utility "identify"; If it does
not exist, quit the script with error.
* Test the existence of image folder;  If it does not exist, quit the
script with error.
* Expand aliases and run .bashrc explicitly if the script is not run
from an interactive shell in order to get paths such as
/usr/local/bin/ on $PATH so the availability test
"hash identify 2>/dev/null" work;
* Added various INFO, DEBUG, and ERROR printing.
* Improved the logic for determing if a file name needs to have extension
added, i.e. iff new extension and current extension are NOT same.

Signed-off-by: Meng Lu <lumeng.dev@gmail.com>
+ added a bash script to send notification at command-line

Signed-off-by: Meng Lu <lumeng.dev@gmail.com>
+ added script to use diffmerge as tool for 'git difftool'

Signed-off-by: Meng Lu <lumeng.dev@gmail.com>
+ added checkstyle configuration file used in Robert Sedgewick's course "Algorithms".

Signed-off-by: Meng Lu <lumeng.dev@gmail.com>
+ added python CLI for WolframAlpha via API request
+ added .gitignore and .idea/ to repo. Removed *.pyc file.

Signed-off-by: Meng Lu <lumeng.dev@gmail.com>
- Removed *.pyc file.

Signed-off-by: Meng Lu <lumeng.dev@gmail.com>