Lookup plugin

[carrascomj]

Closes #35

Description

Allow for a promptSearch like in xmonad. Adds the lookup FLAG:

-L, --lookup
            The input in the prompt will be used as the search term in the selected engine (duckduckgo as default). XDG-
            OPEN will be used for opening the  links.

With the engine OPTION:

--engine <engine>
            Engine to look up into. Possible values: ["github", "rust", "archwiki", "ddg", "english"]. More engines can
            be added at lookup/main.rs

The usage accepts any of the following:

• echo ddg | dmenu --lookup will search the input from the prompt at duckduckgo.
• dmenu --engine=github --lookup will search the input from the prompt at github.
• dmenu_run --engine=rust --lookupwill search the input from the input at rust std docs using dmenu_run.

Implementation

A HashMap with once_cell is used for the mappings from the input to the engine.

• not optimal because it allocates Strings as keys, but I was banging my head against a wall trying to get it to work with &'static str.
• The reasoning behind this pattern is that the interested users could just add/remove entries to use the engines of their likings.
• It uses once_cell instead of lazy_static because the build stage was having problems to resolve the dependencies with dmenu and the plugin.

[Shizcow]

I'm impressed with how seamless this plugin is. Thanks for your contribution!

You mentioned lazy_static having some problems, which I'm not surprised about. I think phf::map could make things more optimal, but that increases dependency count by a lot. Then again this project already has ~300 dependencies when fully loaded anyway so I don't care either way.

I see you're still making some tweaks so I'll merge tomorrow morning. Minor changes I'd love (but can totally do myself):

• Search engines: can we get docs.rs and crates.io?
• Error message on invalid engine: something like Invalid search engine 'dd'. Valid options are: 'ddg', 'archwiki', and 'rust' instead of the current invalid engine

[carrascomj]

Cool! I implemented your suggestions and it is ready from my side. Feel free to change whatever you want (maybe you prefer other names for the engines, I just picked whatever was easy to read).

[Shizcow]

Thanks for the edits. Looking forward to putting echo -e "crates\ngithub\nrust\nddg\nenglish\ndocs\narchwiki" | dmenu | dmenu --lookup somewhere is my dotfiles :+1:

[Shizcow]

After a week of frequent use, I've addressed minor areas of improvement. Everything's documented in make plugins and dmenu --help, but here's an overview:

• Added --list-engines
• Moved from once_cell to phf
• Changed search engine syntax to include %s, similar to how most browsers work
• Documentation edits
• Changed english to dictionary and added thesaurus for completion

This now simplifies the lookup command in my previous comment to:

dmenu --lookup --list-engines | dmenu | dmenu --lookup

[carrascomj]

That's very convenient, I like it :+1: