Return Errors instead of Panicing (#30)

* Return Errors instead of Panicing

- closes #28
- closes #4

Return errors and have the application decide how they want to handle panicing :smile

Signed-off-by: Marko Baricevic <marbar3778@yahoo.com>

* more error changes to prefix and mem dbs

* added errors to other dbs and tests pass

* linting and testing fixes

* add go mod verify to linting

* minor cleanup and changes added to cleveldb

* return error from Has()`

* address some PR comments

* some minor touch up on returning errors

* remvoe .vscode from .gitignore

* error: wraped some errors and comment

- add comment about why the error is ignored
- wraped a couple of errors with error.Wrap

* bring back expect in test case

* add error to iterator and reverse iterator

* add changelog entry

.gitignore

@@ -11,5 +11,4 @@
 # Output of the go coverage tool, specifically when used with LiteIDE
 *.out
 
-/.vscode
 .idea

.golangci.yml

@@ -44,3 +44,7 @@ linters-settings:
   maligned:
     # print struct with more effective memory layout or not, false by default
     suggest-new: true
+  errcheck:
+    # report about assignment of errors to blank identifier: `num, _ := strconv.Atoi(numStr)`;
+    # default is false: such cases aren't reported by default.
+    check-blank: true

CHANGELOG.md

@@ -1,5 +1,33 @@
 # Changelog
 
+## Unreleased
+
+### BREAKING CHANGES
+
+- [\#30](https://github.com/tendermint/tm-db/pull/30) Interface Breaking, Interfaces return errors instead of panic:
+  - Changes to function signatures:
+    - DB interface:
+      - `Get([]byte) ([]byte, error)`
+      - `Has(key []byte) (bool, error)`
+      - `Set([]byte, []byte) error`
+      - `SetSync([]byte, []byte) error`
+      - `Delete([]byte) error`
+      - `DeleteSync([]byte) error`
+      - `Iterator(start, end []byte) (Iterator, error)`
+      - `ReverseIterator(start, end []byte) (Iterator, error)`
+      - `Close() error`
+      - `Print() error`
+    - Batch interface:
+      - `Write() error`
+      - `WriteSync() error`
+    - Iterator interface:
+      - `Next() error`
+      - `Key() (key []byte, err error)`
+      - `Value() (value []byte, err error)`
+
+
+### IMPROVEMENTS
+
 ## 0.3
 
 **2019-11-18**