Parse strict mode from paket.dependencies
Write strict mode into lockfile
Parse strict mode from paket.lock
Implement strict mode - fixes #38
Adding some docs for the strict mode
Merge branch 'strict'

Conflicts:
	src/Paket/DependenciesFile.fs
	src/Paket/LockFile.fs
	src/Paket/Process.fs
	tests/Paket.Tests/DependenciesFile/ParserSpecs.fs
	tests/Paket.Tests/Lockfile/GeneratorSpecs.fs
	tests/Paket.Tests/Lockfile/GeneratorWithMutlipleSourcesSpecs.fs
	tests/Paket.Tests/Lockfile/ParserSpecs.fs
	tests/Paket.Tests/Lockfile/ParserWithMultipleSourcesSpecs.fs