Migrate to RxJava 3

[MrAsterisco]

This PR introduces the following update: support for RxJava 3 (potentially closing #365 ).

I wanted to use ReactiveNetwork in a new project that targets RxJava 3, so I figured I might as well make the transition myself.

A few major things have changed:

• I have changed the package name to "rx3".
• The Build Tools are now on "29.0.2" to support the new Gradle plugin in Android Studio 4.
• Gradle version is now at "6.3".
• The onError method of the NetworkObservingStrategy interface is now using a Throwable instead of a simple Exception. This had to be changed because a lot of methods inside the various implementations of the interface can throw a generic Throwable.
• The android.enableUnitTestBinaryResources has been removed because it is no longer supported.

The rest of the changes are just related to the new version of RxJava (mainly changing the package references).

All unit tests pass, all code styles checks pass. Both example apps work perfectly (I had to add the Java compatibility option to the Kotlin app to make it build). The build on Travis works.

Please, let me know if you're interested in merging this PR and, if so, what would be the next steps.

[codecov-commenter]

Codecov Report

Merging #441 into RxJava3.x will increase coverage by 0.22%.
The diff coverage is 77.14%.

@@               Coverage Diff               @@
##             RxJava3.x     #441      +/-   ##
===============================================
+ Coverage        83.36%   83.59%   +0.22%     
- Complexity         118      131      +13     
===============================================
  Files               11       11              
  Lines              457      451       -6     
  Branches            38       36       -2     
===============================================
- Hits               381      377       -4     
+ Misses              51       49       -2     
  Partials            25       25              

Impacted Files	Coverage Δ	Complexity Δ
...hen/reactivenetwork/library/rx3/Preconditions.java	86.66% <ø> (ø)	12.00 <0.00> (?)
...n/reactivenetwork/library/rx3/ReactiveNetwork.java	83.33% <ø> (ø)	11.00 <0.00> (?)
.../internet/observing/error/DefaultErrorHandler.java	100.00% <ø> (ø)	2.00 <0.00> (?)
.../strategy/PreLollipopNetworkObservingStrategy.java	63.33% <63.33%> (ø)	8.00 <8.00> (?)
...chen/reactivenetwork/library/rx3/Connectivity.java	68.14% <66.66%> (ø)	24.00 <12.00> (?)
.../strategy/MarshmallowNetworkObservingStrategy.java	98.38% <90.00%> (ø)	22.00 <1.00> (?)
...tivenetwork/library/rx3/ConnectivityPredicate.java	100.00% <100.00%> (ø)	7.00 <4.00> (?)
.../internet/observing/InternetObservingSettings.java	96.15% <100.00%> (ø)	12.00 <1.00> (?)
...ving/strategy/SocketInternetObservingStrategy.java	94.11% <100.00%> (ø)	11.00 <3.00> (?)
...trategy/WalledGardenInternetObservingStrategy.java	95.91% <100.00%> (ø)	15.00 <3.00> (?)
... and 2 more

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[pwittchen]

Hi @MrAsterisco,

Thanks for this PR!

Could you please squash your commits into one and set target branch to RxJava3.x? I know it didn't exist before, but I just created it and I'd like to have changes related to RxJava3.x on that branch and RxJava2.x should contain code depending on RxJava2.x only.

Regards,
Piotr

[pwittchen]

I already changed target branch (base) to RxJava3.x. I found out it was possible in this PR.

[MrAsterisco]

Ok, great! Before squashing my commits, would you like me to go through the process of updating the Changelog file and generating the new documentation?

[pwittchen]

You can update changelog and documentation in README.md file. I'll need to update JavaDocs and website on gh-pages later separately because that's another branch.

[MrAsterisco]

Ok, done! I'm assuming that this will be a 4.0.0, since there is a (small) breaking change in the NetworkObservingStrategy interface.

[pwittchen]

Changes look fine. I have a few issues with the documentation in README.md. Moreover, I have a question: Did you use code formatter / code style described here: https://github.com/pwittchen/ReactiveNetwork#code-style ? If not, then please apply it and reformat code with it.

[MrAsterisco]

OK! I've reformatted the code using the AndroidSquare style (about 30 files were not formatted correctly) and I've also updated the README as you asked (I've also changed the references to the RxJava2.x and the name of the artifact).

I noticed there's a Contributors section, so I've added myself in there; hope that's ok.

[pwittchen]

Looks good. There's one more change required for migration to the new RxJava version. In the library/gradle.properties file, we need to change:

POM_ARTIFACT_ID=reactivenetwork-rx2

to:

POM_ARTIFACT_ID=reactivenetwork-rx3

[MrAsterisco]

Done! To be sure, I've also searched for "rx2" in the whole project and I've updated the proguard rules files to point to the correct package.

I've also updated VERSION_NAME and VERSION_CODE in gradle.properties.

[pwittchen]

Merged. It will be available in the next release for RxJava3.x. Thanks for your contribution @MrAsterisco!