Documentation and linting improvements (#108)

* Simplifying documentation for getting started: Removed outdated information about install Golang on different platforms and instead included a link to the official Golang website which has more up to date information. Instructions for installing docker-compose have also been added.

* Added documentation to all exported functions and structs.

* Unexported some structures and functions that were needlessly exported.

* Adding golang CI default configuration which can be useful while developing and may be turned on later in the CI.

* Moving build process in CI to xenial.

* Reducing line size. in some files and shadowing in some test cases.

.golangci.yml

@@ -0,0 +1,71 @@
+# This file contains all available configuration options
+# with their default values.
+
+# options for analysis running
+run:
+  # default concurrency is a available CPU number
+  concurrency: 4
+
+  # timeout for analysis, e.g. 30s, 5m, default is 1m
+  deadline: 1m
+
+  # exit code when at least one issue was found, default is 1
+  issues-exit-code: 1
+
+  # include test files or not, default is true
+  tests: true
+
+  skip-dirs:
+    - gen-go/
+
+# output configuration options
+output:
+  # colored-line-number|line-number|json|tab|checkstyle|code-climate, default is "colored-line-number"
+  format: colored-line-number
+
+  # print lines of code with issue, default is true
+  print-issued-lines: true
+
+  # print linter name in the end of issue text, default is true
+  print-linter-name: true
+
+
+# all available settings of specific linters
+linters-settings:
+  errcheck:
+    # report about not checking of errors in type assetions: `a := b.(MyStruct)`;
+    # default is false: such cases aren't reported by default.
+    check-type-assertions: true
+
+    # 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
+  govet:
+    # report about shadowed variables
+    check-shadowing: true
+  goconst:
+    # minimal length of string constant, 3 by default
+    min-len: 3
+    # minimal occurrences count to trigger, 3 by default
+    min-occurrences: 2
+  misspell:
+    # Correct spellings using locale preferences for US or UK.
+    # Default is to use a neutral variety of English.
+    # Setting locale to US will correct the British spelling of 'colour' to 'color'.
+    locale: US
+  lll:
+    # max line length, lines longer will be reported. Default is 120.
+    # '\t' is counted as 1 character by default, and can be changed with the tab-width option
+    line-length: 120
+    # tab width in spaces. Default to 1.
+    tab-width: 4
+
+linters:
+  enable:
+    - govet
+    - goimports
+    - golint
+    - lll
+    - goconst
+  enable-all: false
+  fast: false