Find and replace w/ regex functionality

[benpage2]

This idea was cooked up in #4571 (although there was a slight bit of confusion at the time) and it was recommended that I make a new thread.

While regex replacement functionality does exist in both the substitute and rewrite plugins, I haven't found an option to directly perform a find and replace on the database and file tags.

So as a proposal, this command/ would act similarly to beet modify and act on the library and tags. Additionally, functionality similar to import-replace could allow users to perform the replacements before autotagging to help strengthen potential matches.

Here's what I dreamed up:

beet replace [options] QUERY find:replace

Similar to QUERY find:replace runs a simple find and replace while find::replace runs a regex find and replace
Running beet replace [options] would run the replacements set under in the config, but without having to run an import .

Options (same as beet modify):

• -M don't move
• -W don't write
• -w write (default)
• -a albums instead of items
• -y skip yes prompt

Additional options:

• -i case insensitive
• -e matches entire word (using -e because "whole word" would intuitively be -w)
• -f specify a field? (I'm not sure if this would be part of the query functionality or should be it's own option)

Config options:

• auto: yes/no run config on import
• case_insensitive: yes/no
• entire_word: yes/no (not "whole word" for clarity as "-w" is already being used)

Additional config ideas from import-replace (quoting mostly from the import-replace readme):

• item_fields is a set of fields to run replacements on for items
• album_fields is a set of fields to run replacements on for albums
• replace is a set of regex/replacement pairs

Overall the config may look like:

pluginname:
    auto: yes
    case_insensitive: no
    entire_word: no
    replacements:
        - item_fields: title
           replace:
               'The':'That' (alternatively `The::'that' would be regex)
        - item_fields: album
        - album_fields: album
            replace:
                'Foo':'Bar'

[benpage2]

@JOJ0 @arsaboo