Dsc

New in this release:

- `dscquery` now properly handles `NULL` module output variables.
- Some performance improvements on I/O and meta-database.
- SoS bumped to version 0.19.7 for bug fixes and improved robustness on cluster job submitter.

- Now SQLite keywords can be used as module names: no error message will be triggered.
- Introduce an explicit syntax for base module: a module without executable is considered base module.
- Bump `rpy2` version requirement version 3.0.0+ for benchmark with R and Python modules.
- SoS bumped to version 0.19.5 for improved memory usage on job submitter and improved Python module version check.

Major improvements to `dscrquery`

- Performance improvement 168
- Output format improvement 174

- Reimplement `dsc-query` and `dscrquery` for improved handling of missing value 145.
- Reimplement `dscrquery`'s `condition` statement to make it more R-user friendly.
- Add unknown command argument 162.
- [minor] Introduce `DSC::run::default`, for the behavior of running the script without targets.
- [minor] 161
- SoS bumped to version 0.19.1 for improved sockets management and improved R library auto-installation.

- [minor] 160
- SoS bumped to version 0.18.4 for performance optimizations

- Various improvements for remote job submission and execution (mostly on SoS).
- SoS bumped to version 0.18.1 to support these changes.