Hbayesdm

* Now, in default, you should build a Stan file into a binary for the first time to use it. To build all the models on installation, you should set an environmental variable `BUILD_ALL` to `true` before installation.
* Now all the implemented models are refactored using `hBayesDM_model` function. You don't have to change anything to use them, but developers can easily implement new model now!
* We added a Kalman filter model for 4-armed bandit task (`bandit4arm2_kalman_filter`; Daw et al., 2006) and a probability weighting function for general description-based tasks (`dbdm_prob_weight`; Erev et al., 2010; Hertwig et al., 2004; Jessup et al., 2008).
* Initial values of parameter estimation for some models are updated as plausible values, and the parameter boundaries of several models are fixed (see more on issue 63 and 64 in Github).
* Exponential and linear models for choice under risk and ambiguity task now have four model regressors: `sv`, `sv_fix`, `sv_var`, and `p_var`.
* Fix the Travix CI settings and related codes to be properly passed.

* Update the dependencies on `rstan` (>= 2.18.1)
* Remove `rstantools` from Imports
* No changes on model files, as same as the version 0.6.2

* Fix an error on choiceRT_ddm (44)

* Solve an issue with built binary files.
* Fix an error on peer_ocu with misplaced parentheses.

* Add new tasks (Balloon Analogue Risk Task, Choice under Risk and Ambiguity Task, Probabilistic Selection Task, Risky Decision Task (a.k.a. Happiness task), Wisconsin Card Sorting Task)
* Add a new model for the Iowa Gambling Task (igt_orl)
* Change priors (Half-Cauchy(0, 5) --> Half-Cauchy(0, 1) or Half-Normal(0, 0.2)
* printFit function now provides LOOIC weights and/or WAIC weights

What's new in v0.5.1.

* Add models for the Two Step task
* Add models without indecision point parameter (alpha) for the PRL task (prl_*_woa.stan)
* Model-based regressors for the PRL task are now available
* For the PRL task & prl_fictitious.stan & prl_fictitious_rp.stan --> change the range of alpha (indecision point) from [0, 1] to [-Inf, Inf]