Dynamic synapses and updates to lessons (including operant conditioning) (#109)

* init commit of exp-syn material

* wrote dynamics for exp-syn

* wrote dynamics for exp-syn

* wrote test for exp-syn

* updates to exp-syn/testing lesson

* modded docs to reflect exp-syn

* integrated alpha-synapse

* integrated alpha-syn, cleaned up exp-syn

* cleaned up alpha/exp syn

* cleaned up help for exp/alpha-syn

* cleaned up help for exp/alpha-syn

* minor tweaks + init of rl-snn exhibit lesson (#108)

Co-authored-by: Alexander Ororbia <[email protected]>

* began draft of dyn-syn lesson

* revised dyn-syn lesson further

* added some text to rl-snn lesson

* cleaned up dyn-syn/lesson

* cleaned up dyn-syn/lesson

* fixed scaling issue in exp/alpha syn

* update to docs

* cleaned up neurocog tutorials on plasticity

* cleaned up dyn-syn lesson

* cleaned up dyn-syn lesson

* integrated double-exp syn model

* mod to dyn-syn lesson

* finished v1 of rat-maze rl-snn

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Co-authored-by: Alexander Ororbia <[email protected]>

Author: ago109