Rephrase "assigning/binding to rvalue" errors to include context (#119) (#123)

* Rephrase "assigning/binding to rvalue" error messages with context (#119)

* Fix code style in parser/lval.js

* istanbul ignore some unused branches in parser/lval.js

* Fix code style again in parser/lval.js

test/fixtures/esprima/invalid-syntax/migrated_0045/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:0)"
+  "throws": "Invalid left-hand side in assignment expression (1:0)"
 }

test/fixtures/esprima/invalid-syntax/migrated_0046/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:0)"
+  "throws": "Invalid left-hand side in assignment expression (1:0)"
 }

test/fixtures/esprima/invalid-syntax/migrated_0047/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:1)"
+  "throws": "Invalid left-hand side in assignment expression (1:1)"
 }

test/fixtures/esprima/invalid-syntax/migrated_0052/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:0)"
+  "throws": "Invalid left-hand side in postfix operation (1:0)"
 }

test/fixtures/esprima/invalid-syntax/migrated_0053/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:0)"
+  "throws": "Invalid left-hand side in postfix operation (1:0)"
 }

test/fixtures/esprima/invalid-syntax/migrated_0054/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:2)"
+  "throws": "Invalid left-hand side in prefix operation (1:2)"
 }

test/fixtures/esprima/invalid-syntax/migrated_0055/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:2)"
+  "throws": "Invalid left-hand side in prefix operation (1:2)"
 }

test/fixtures/esprima/invalid-syntax/migrated_0056/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:5)"
+  "throws": "Invalid left-hand side in for-in statement (1:5)"
 }

test/fixtures/esprima/invalid-syntax/migrated_0066/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:0)"
+  "throws": "Invalid left-hand side in assignment expression (1:0)"
 }

test/fixtures/esprima/invalid-syntax/migrated_0067/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:0)"
+  "throws": "Invalid left-hand side in assignment expression (1:0)"
 }

test/fixtures/esprima/invalid-syntax/migrated_0098/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:1)"
+  "throws": "Invalid left-hand side in arrow function parameters (1:1)"
 }

test/fixtures/esprima/invalid-syntax/migrated_0099/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:1)"
+  "throws": "Invalid left-hand side in arrow function parameters (1:1)"
 }

test/fixtures/esprima/invalid-syntax/migrated_0125/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:5)"
+  "throws": "Invalid left-hand side in for-in statement (1:5)"
 }

test/fixtures/esprima/invalid-syntax/migrated_0126/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Assigning to rvalue (1:5)"
+  "throws": "Invalid left-hand side in for-in statement (1:5)"
 }