Low performance to get feeds

[gandf]

Performance are low when read feeds.

Test with 8 differents feeds: Fetch time take 20ms to 675ms : time Parse time : 571 ms to 16,5s

=> must optimise parse

[gandf]

After profiling, issue is localised in common-worker.js. SearchTags and SearchTag have search depth of 30. In reality, search depth for:

• SearchTags : max 6
• SearchTag : max 4

These results may be different depending on feeds.

I set these value to have some leeway

• SearchTags : max 8
• SearchTag : max 5

I add options to allow users to use more complex feeds without issue or to allow feeds parse speed to be optimized as tight as possible.

[gandf]

Same test with 6 & 4 value for max level: Parse time : 8ms to 22ms

In summary : Down from 16,5s max to 22ms max

[gandf]

Close by commit c4c8f7b