Hbayesdm

* Support variational Bayesian methods (vb=TRUE)
* Allow posterior predictive checks, except for drift-diffusion models (inc_postpred=TRUE)
* Add the peer influence task (Chung et al., 2015, USE WITH CAUTION for now and PLEASE GIVE US FEEDBACK!)
* Add 'prl_fictitious_rp' model
* Made changes to be compatible with the newest Stan version (e.g., // instead of for commenting).
* In 'prl_*' models, 'rewlos' is replaced by 'outcome' so that column names and labels would be consistent across tasks as much as possible.
* Email feature is disabled as R mail package does not allow users to send anonymous emails anymore.
* When outputs are saved as a file (*.RData), the file name now contains the name of the data file.

* Add a choice reaction time task and evidence accumulation models
- Drift diffusion model (both hierarchical and single-subject)
- Linear Ballistic Accumulator (LBA) model (both hierarchical and single-subject)
* Add PRL models that can fit multiple blocks
* Add single-subject versions for the delay discounting task (`dd_hyperbolic_single` and `dd_cs_single`).
* Standardize variable names across all models (e.g., `rewlos` --> `outcome` for all models)
* Separate versions for CRAN and GitHub. All models/features are identical but the GitHub version contains precompilled models.

- Remove dependence on the modeest package. Now use a built-in function to estimate the mode of a posterior distribution.
- Rewrite the "printFit" function.

- Made several changes following the guidelines for R packages providing interfaces to Stan.
- Stan models are precompiled and models will run immediately when called.
- The default number of chains is set to 4.
- The default value of adapt_delta is set to 0.95 to reduce the potential for divergences.
- The printFit function uses LOOIC by default. Users can select WAIC or both (LOOIC & WAIC) if needed.