YAML config can be loaded from sub includes, thus reduces the main YAML size

[azagniotov]

This PR resolves issue #145

[codecov-io]

Codecov Report

Merging #152 (5abc29a) into master (da71d0b) will increase coverage by 0.07%.
The diff coverage is 95.00%.

@@             Coverage Diff              @@
##             master     #152      +/-   ##
============================================
+ Coverage     95.92%   96.00%   +0.07%     
- Complexity      582      585       +3     
============================================
  Files            51       51              
  Lines          1840     1851      +11     
  Branches        179      181       +2     
============================================
+ Hits           1765     1777      +12     
+ Misses           63       61       -2     
- Partials         12       13       +1     

Impacted Files	Coverage Δ	Complexity Δ
.../io/github/azagniotov/stubby4j/yaml/SnakeYaml.java	100.00% <ø> (ø)	3.00 <0.00> (ø)
...io/github/azagniotov/stubby4j/yaml/YamlParser.java	99.27% <94.11%> (-0.73%)	43.00 <4.00> (+3.00)	⬇️
.../github/azagniotov/stubby4j/utils/StringUtils.java	98.73% <100.00%> (+2.43%)	60.00 <1.00> (ø)
...niotov/stubby4j/yaml/ConfigurableYAMLProperty.java	100.00% <100.00%> (ø)	7.00 <0.00> (ø)