Add new DecFileParser class, with test suite (#21)

* Add new DecFileNotParsed class, with test suite

* [skip ci] More functionality and doc to DecFileParser class and related helper functions

* Method added to build a complete decay chain. More doc on DecFileParser class

* [skip-ci] Add missing model to decfile.lark

* Add more tests

* Clean up tox

* Fix Python < 3.6, add __slots__

* Add new DecFileNotParsed class, with test suite

* [skip ci] More functionality and doc to DecFileParser class and related helper functions

* Method added to build a complete decay chain. More doc on DecFileParser class

* [skip-ci] Add missing model to decfile.lark

* Add more tests

decaylanguage/data/decfile.lark

@@ -44,7 +44,7 @@ model_options : (value | LABEL)+
 _NEWLINE: ( /\r?\n[\t ]*/ | COMMENT )+
 
 // We must set priorities here to use lalr - match model name above label, and label above something else
-MODEL_NAME.2 : "BaryonPCR"|"BTO3PI_CP"|"BTOSLLALI"|"BTOSLLBALL"|"BTOXSGAMMA"|"BTOXSLL"|"CB3PI-MPP"|"CB3PI-P00"|"D_DALITZ"|"ETA_DALITZ"|"GOITY_ROBERTS"|"HELAMP"|"HQET"|"ISGW2"|"OMEGA_DALITZ"|"PARTWAVE"|"PHSP"|"PI0_DALITZ"|"PYTHIA"|"SLN"|"STS"|"SVP_HELAMP"|"SVS"|"SVV_HELAMP"|"TAUHADNU"|"TAULNUNU"|"TAUSCALARNU"|"TAUVECTORNU"|"TSS"|"TVS_PWAVE"|"VLL"|"VSP_PWAVE"|"VSS"|"VSS_BMIX"|"VUB"|"VVP"|"VVPIPI"|"VVS_PWAVE"
+MODEL_NAME.2 : "BaryonPCR"|"BTO3PI_CP"|"BTOSLLALI"|"BTOSLLBALL"|"BTOXSGAMMA"|"BTOXSLL"|"CB3PI-MPP"|"CB3PI-P00"|"D_DALITZ"|"ETA_DALITZ"|"GOITY_ROBERTS"|"HELAMP"|"HQET"|"ISGW2"|"OMEGA_DALITZ"|"PARTWAVE"|"PHSP"|"PI0_DALITZ"|"PYTHIA"|"SLN"|"STS"|"SVP_HELAMP"|"SVS"|"SVV_HELAMP"|"TAUHADNU"|"TAULNUNU"|"TAUSCALARNU"|"TAUVECTORNU"|"TSS"|"TVS_PWAVE"|"VLL"|"VSP_PWAVE"|"VSS"|"VSS_BMIX"|"VUB"|"VVP"|"VVPIPI"|"VVS_PWAVE"|"SSD_CP"
 
 LABEL : /[a-zA-Z0-9\/\-+*_()']+/
 COMMENT : /[;#][^\n]*/
@@ -53,4 +53,4 @@ COMMENT : /[;#][^\n]*/
 %ignore COMMENT
 
 // Disregard spaces in text
-%ignore WS_INLINE
+%ignore WS_INLINE