Adds an option to make a column to contain datasheet links

[set-soft]

Replaces #79

Description

Having a separated column for the datasheet is an overkill. We can make that another column contains this information as a link. The part number is a suitable column.

This patch allows configuring it.

How to use

Define the datasheet_as_link option in the configuration file (i.e. bom.ini).

The value for this option is the column you want to convert into a link to the datasheet. Example:

datasheet_as_link = manf#

This will make entries in the column manf# (manufacturer part number) links to the datasheet.

Limitations

Only available for HTML

[set-soft]

Rebased it so it can cleanly apply. I saw a chunk of code missing from the "digikey_link_2" patch, but I plan to fix it with anoter PR. But I need this merged or the other will be pure conflicts ;-)

[SchrodingersGat]

Hi @set-soft please fix issues with preferences.py cheers

[set-soft]

Hi @SchrodingersGat ! Ok, I did a rebase using your current HEAD. Solved the conflict with ref_separator now you should be able to apply it.

[SchrodingersGat]

Thanks @set-soft - looks like there's a small style error though - https://travis-ci.org/github/SchrodingersGat/KiBoM/jobs/758740224

[set-soft]

Hi @SchrodingersGat ! I didn't notice the https://travis-ci.org/github/SchrodingersGat/KiBoM/jobs/758740224 link, and now the logs are gone. Running flake8 on my system doesn't report errors.

[SchrodingersGat]

@set-soft yeah this one is from a while ago. As it is passing now, I'm happy to merge it in.