Add method to include accounts resolve param

[paultyng]

Unsure what is the preferred way to add params that aren't currently exposed. Would you prefer a variadic parameter with modifiers or something, or just add additional methods like this? There is another param missing but I didn't need it for my usecase: following: https://docs.joinmastodon.org/methods/accounts/

[mattn]

Could you please add test?

[codecov-commenter]

Codecov Report

Base: 87.16% // Head: 87.28% // Increases project coverage by +0.12% :tada:

Coverage data is based on head (f610598) compared to base (7dfe81e). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #150 +/- ## ========================================== + Coverage 87.16% 87.28% +0.12% ========================================== Files 15 15 Lines 935 944 +9 ========================================== + Hits 815 824 +9 Misses 75 75 Partials 45 45 ``` | [Impacted Files](https://codecov.io/gh/mattn/go-mastodon/pull/150?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mattn) | Coverage Δ | | |---|---|---| | [accounts.go](https://codecov.io/gh/mattn/go-mastodon/pull/150/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mattn#diff-YWNjb3VudHMuZ28=) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mattn). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mattn)

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[mattn]

Sorry, test already exists.

[mattn]

Could you please fix conflicts?