Implement alt-link and bind it to ^o

[lyricnz]

Add support for an "alternate link" for a coin, to a user-defined target. This is expressed in a code snippet, defined in the config.toml file. The code has access to sprintf and a coin object with [ID, Name, Symbol, Rank, Slug] available.

alt_link_code = "sprintf(\"https://www.tradingview.com/chart/?symbol=%sUSDT\", coin.Symbol)"

Per #283

[lyricnz]

Thoughts:

• signature of interface.CoinLink() and interface.AltCoinLink() are different - they should probably be the same
• in fact, CoinLink should probably just be a pre-configured example of the same pattern
• in fact, we could probably support an arbitrary number of CoinLinks (though managing config would be a pain)
• the config should probably be in an api-specific section, but updating config structs gives me a headache

[lyricnz]

The config is a little codey. Might be easier to explain with simple tokens.

[miguelmota]

(copying my comment from discord):

This format makes it very specific to Go but the config file should be generalized. I think something like alt_link_code = "https://www.tradingview.com/chart/?symbol=:SYMBOL:" would be better and we can offer :SYMBOL:, :NAME, :ID: , etc as variables

[miguelmota]

Merging this with some changes

I updated it to use template tags and simplified the link generation by not passing the alt coin link code to each coin api class

Example link

alt_coin_link = "https://www.tradingview.com/symbols/{{SYMBOL}}USD/"

Available tags:

• {{ID}}
• {{NAME}}
• {{RANK}}
• {{SLUG}}
• {{SYMBOL}}

Thanks @lyricnz!