Replace objects with Maps to ensure compatibility with Hermes

[danii1]

This PR replaces objects with Map to alleviate the issue with Hermes runtime(React Native) that doesn't support a large number of props in an object. This allows to use this package in React Native apps.

Related issue:
#168

[Rycochet]

This needs to compare with #98 and have a look at any side effects etc mentioned - not got time to review myself now, but of the general opinion that it's worth adding :-)

[danii1]

I have another branch with the same changes applied to v2: https://github.com/DISCO-team/lz-string/tree/feature/object-map

Ran test:bench, Map seems faster in most scenarios(particularly where it matters like compressing large text), not surprising given it's optimized for addition and deletion:
obj.txt
map.txt

Changes in this PR are straightforward and simpler than in #98

[adbs1]

@Rycochet @danii1 Any further progress likely here? The changes look trivial with a cursory glance :)

[karnthis]

The change is solid and has my vote of support from a code standpoint, but needs a final decision from a compatibility angle. LZ-String has been maintaining compatibility with anything javascript released since roughly 2012, and this change will break that trend. I believe there is a limit to backwards compatibility and a move to v2 is a good time to revisit that support, but is ultimately not my decision to make. @Rycochet @pieroxy what are your thoughts?