Consider adding executed commands to shell history

[alexilyaev]

First mentioned in #8
Then recently requested again by @julienben

I didn't want to pursue this path due to he complexity of finding the relevant history file for each shell and supporting different history formats and OS's.
But maybe we could satisfy most users using existing utils:
https://github.com/sindresorhus/shell-history

Relevant environment variables:

• SHELL - Current used shell (e.g. bash, zsh)
• HISTFILE - Path to history file (ref http://tldp.org/LDP/abs/html/histcommands.html)

Known history file locations:

• $HOME/.bash_history
• $HOME/.zsh_history
• $HOME/.zhistory (legacy or Oh My Zsh variant or something)
• fish - history file location fish-shell/fish-shell#862