Initial MultiPlatform (JVM+JS)

Convert to multiplatform (#21)

* update gradle v6.3 -> v6.7.1

* update khex v0.6 -> v1.0.0

* add build config to gradle.properties

* add symbolic link to gradle.properties under buildSrc

* add mpp-module.gradle.kts

* add khex as a commonTest dependency

* enable 'InlineClasses' language feature for all test sourcesets

* add common tests config to mpp-module.gradle.kts

* allow gradual conversion of submodules to MPP

* use 'mavenLocal' deployment of MPP khex temporarily

* increase tests timeout for nodeJS

* TODO: enable strict 'explicitApi'

* convert Keccak submodule to MPP (depend on com.ionspin.kotlin:bignum for MPP BigInteger)

* update kotlin v1.4.21 -> v.1.4.30

* update bignum v0.2.4-SNAPSHOT -> v0.2.4 (stable)

* convert ripemd160 module to multiplatform

* convert sha256 module to multiplatform

* convert sha512 module to multiplatform

* remove non-multiplatform subprojects config

* define dependency versions in Versions.kt

* enabled strict 'explicitApi' mode

* added compilation options for js

* update gradle v6.7.1 -> v6.8.1

* set jvm target to 1.8 (default is 1.6)

* simplify test tasks logging config

* fetch KHex from GitHub Packages

* config dependencyResolutionManagement in settings.gradle.kts

* add comment for the GitHub Packages public access workaround

* fix KHex dependency group name

* add aggregate test report task to root project

* fix KHex dependency groupId

* add GitHub Actions workflows

* swap names of workflows

* add 'maven-publish' with Github Packages config

* increase mocha test timeout to 300s

* update 'com.ionspin.kotlin:bignum' v0.2.4 -> v0.2.8

* use KHex from GitHub Packages of the origin repo

* update gradle v6.8.1 -> v6.8.2

* update KHex vmaster-SNAPSHOT -> v1.1.0

* update README.md

* remove 'version' from gradle.properties