feat(config): add incremental option

[ahnpnl]

• Add incremental option to ts-jest config to turn on/off Incremental Program vs Program.
• Add doc for new option compilerHost and incremental.
• Improve e2e tests and unit tests.

[coveralls]

Pull Request Test Coverage Report for Build 4095

• 11 of 11 (100.0%) changed or added relevant lines in 3 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.6%) to 92.21%

---

Files with Coverage Reduction	New Missed Lines	%
src/compiler/language-service.ts	1	89.66%
src/ts-jest-transformer.ts	1	87.6%

Totals
Change from base Build 4093:	0.6%
Covered Lines:	1138
Relevant Lines:	1179

---

💛 - Coveralls