create CustomError to refactor other Error classes

[rbecheras]

Fix #22

[coveralls]

Coverage decreased (-3.3%) to 96.721% when pulling d8b2e66 on 22-resolve-code-climate-issues into aab7947 on master.

[coveralls]

Coverage decreased (-2.4%) to 97.581% when pulling 7b45832 on 22-resolve-code-climate-issues into aab7947 on master.

[coveralls]

Coverage decreased (-12.0%) to 88.0% when pulling fb77e22 on 22-resolve-code-climate-issues into aab7947 on master.

[coveralls]

Coverage decreased (-15.0%) to 85.0% when pulling 9ffd8a4 on 22-resolve-code-climate-issues into aab7947 on master.

[coveralls]

Coverage decreased (-15.0%) to 85.0% when pulling 9ffd8a4 on 22-resolve-code-climate-issues into aab7947 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 2014eac on 22-resolve-code-climate-issues into aab7947 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 2014eac on 22-resolve-code-climate-issues into aab7947 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 1a96f64 on 22-resolve-code-climate-issues into aab7947 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 97b6890 on 22-resolve-code-climate-issues into aab7947 on master.