Add md5sum function to crypto library

[inFocus7]

Add an md5sum function to list of supported crypto functions.
Add .idea to gitignore, because I use JetBrains (can remove if not needed).

#419

[io41]

Please remove. Developer specific files don't belong here.

Use git config --global core.excludesfile $HOME/.gitignore instead.

Which file to place a pattern in depends on how the pattern is meant to be used.

Patterns which should be version-controlled and distributed to other repositories via clone (i.e., files that all developers will want to ignore) should go into a .gitignore file.

Patterns which are specific to a particular repository but which do not need to be shared with other related repositories (e.g., auxiliary files that live inside the repository but are specific to one user’s workflow) should go into the $GIT_DIR/info/exclude file.

Patterns which a user wants Git to ignore in all situations (e.g., backup or temporary files generated by the user’s editor of choice) generally go into a file specified by core.excludesFile in the user’s ~/.gitconfig. Its default value is $XDG_CONFIG_HOME/git/ignore. If $XDG_CONFIG_HOME is either not set or empty, $HOME/.config/git/ignore is used instead.

-- https://git-scm.com/docs/gitignore