Added line drawing functionality to the library.

[pubudug]

First of all thanks for the library and the tutorials at http://www.redblobgames.com/, which inspired me to contribute :).

This PR contains the following Added line drawing functionality to the library. Added a unit test to test the functionality. Added functionality to the SWT example to show this feature.

Let me know if there is anything that needs to change in my commits.

[adam-arold]

Hi there!

Travis complained about the PR. I think there are some checkstyle violations:

[INFO] There are 10 errors reported by Checkstyle 6.11.2 with checkstyle.xml ruleset.
[ERROR] src/main/java/org/codetome/hexameter/core/api/HexagonalGridCalculator.java:[63] (javadoc) SummaryJavadoc: First sentence of Javadoc is incomplete (period is missing) or not present.
[ERROR] src/main/java/org/codetome/hexameter/core/internal/impl/HexagonalGridCalculatorImpl.java:[86,28] (naming) LocalVariableName: Local variable name 'h' must match pattern '^[a-z][a-z0-9][a-zA-Z0-9]*$'.
[ERROR] src/main/java/org/codetome/hexameter/core/internal/impl/HexagonalGridCalculatorImpl.java:[93,97] (naming) ParameterName: Parameter name 't' must match pattern '^[a-z][a-z0-9][a-zA-Z0-9]*$'.
[ERROR] src/main/java/org/codetome/hexameter/core/internal/impl/HexagonalGridCalculatorImpl.java:[99,63] (naming) ParameterName: Parameter name 't' must match pattern '^[a-z][a-z0-9][a-zA-Z0-9]*$'.
[ERROR] src/main/java/org/codetome/hexameter/core/internal/impl/HexagonalGridCalculatorImpl.java:[103,57] (naming) ParameterName: Parameter name 'x' must match pattern '^[a-z][a-z0-9][a-zA-Z0-9]*$'.
[ERROR] src/main/java/org/codetome/hexameter/core/internal/impl/HexagonalGridCalculatorImpl.java:[103,67] (naming) ParameterName: Parameter name 'y' must match pattern '^[a-z][a-z0-9][a-zA-Z0-9]*$'.
[ERROR] src/main/java/org/codetome/hexameter/core/internal/impl/HexagonalGridCalculatorImpl.java:[103,77] (naming) ParameterName: Parameter name 'z' must match pattern '^[a-z][a-z0-9][a-zA-Z0-9]*$'.
[ERROR] src/main/java/org/codetome/hexameter/core/internal/impl/HexagonalGridCalculatorImpl.java:[108,16] (naming) LocalVariableName: Local variable name 'x_diff' must match pattern '^[a-z][a-z0-9][a-zA-Z0-9]*$'.
[ERROR] src/main/java/org/codetome/hexameter/core/internal/impl/HexagonalGridCalculatorImpl.java:[109,16] (naming) LocalVariableName: Local variable name 'y_diff' must match pattern '^[a-z][a-z0-9][a-zA-Z0-9]*$'.
[ERROR] src/main/java/org/codetome/hexameter/core/internal/impl/HexagonalGridCalculatorImpl.java:[110,16] (naming) LocalVariableName: Local variable name 'z_diff' must match pattern '^[a-z][a-z0-9][a-zA-Z0-9]*$'.

Seems like it has problems with your variable naming convention and the javadoc. It should be trivial to fix. I'd suggest using maven to build the project: mvn clean install should do it from the root of the project.

Thank you for your contribution!

[adam-arold]

I've checked the code and it looks cool!

[codecov-io]

Current coverage is 90.55%

Merging #23 into master will increase coverage by 0.30%

@@             master        #23   diff @@
==========================================
  Files            19         19          
  Lines           359        381    +22   
  Methods           0          0          
  Messages          0          0          
  Branches         64         67     +3   
==========================================
+ Hits            324        345    +21   
  Misses           16         16          
- Partials         19         20     +1   

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[adam-arold]

Please note that I did not write the tutorials at redblobgames! I simply used it to implement this library. :)

[pubudug]

Ah ok. I made the assumption because this library was linked from that page :).