Incomplete implementation of partial functions

[aeberhart]

We have some problems wrt. to partial functions:

• partial functions keep the signature of the base function (see Incorrect each function signature validation #79)
• bug in

  jsonata-java/src/main/java/com/dashjoin/jsonata/Jsonata.java

  Line 1844 in 0b40af3

  if (arg.type.equals("operator") && (arg.value.equals("?"))) {

  , arg.value is char and comparison will always be false
• partial function derived from custom function (see Custom function pipe error #83)
• we re-use the base function for partial functions (see incorrect result when $map($, $append(?)) #86)
• there are some TODOs which we did not yet implement because of the lack of unit test coverage (

  jsonata-java/src/main/java/com/dashjoin/jsonata/Jsonata.java

  Line 1839 in 78ce14c

  if (Functions.isLambda(proc)) {

  )