Support seq and maps (rebase of #142, refactor of #129)

[joemat]

Based on #142 and #129 this PR adds support to serialize maps and vectors. See description of #142 for details.

This is just a rebased version of #142 which fixes the merge conflict.

Kudos to @adrianbenavides and @Niedzwiedzw for their work on this.

[ghost]

Closes #135.

[ghost]

FYI, I've contributed to and find this project useful and so proposed we move it to a group: #155.

[XiaoXiaoSN]

Hi, I noticed this awesome job. But it seems to have been around for a while and has some conflicts from the master branch.

Would you complete this Pull Request? Or if possible I can also take over and resolve the conflicting part.

[victorpaleologue]

Hi, I noticed this awesome job. But it seems to have been around for a while and has some conflicts from the master branch.

Would you complete this Pull Request? Or if possible I can also take over and resolve the conflicting part.

FTR you did the rebase here #170, thanks.

[wt]

Should this be closed because of #173? #170 says that #173 merges the changes from some other changes including this one.

[joemat]

yes, makes sense to close this one then