Improve overloads and types

[elchininet]

This pull request improves the TypeScript support and the flexibility of the API adding more methods overloads and allowing to accept also strings in the enum parameters. Also some bugs have been fixed.

The next changes are the main changes that have been applied:

1. For methods that use Mix and Harmony enums, now it is possible to send also string values.

2. Make optional the shades and tints parameters of the getShades and getTints methods respectively (the default will be 5)

3. getBlendStatic methods now have two overloads

getBlendColorsStaticMethod(
  fromColor: string | object,
  toColor: string | object,
  options?: Options
)

// Specifying the number of steps
getBlendColorsStaticMethod(
  fromColor: string | object,
  toColor: string | object,
  steps: number,
  options?: Options
)

4. getMixStatic methods now have two overloads

getMixColorsStaticMethod(
  colors: [string | object][],
  options?: Options
)

// Specifying the mix mode
getMixColorsStaticMethod(
  colors: [string | object][],
  mode: 'ADDITIVE' | 'SUBTRACTIVE',
  options?: Options
)

5. getHarmony method now have four overloads for each color input

// If harmony is not sent, the default will be "COMPLEMENTARY"
// If mode is not sent, the default will be "ADDITIVE"
getHarmony(
  color: string | object,
  options?: Options
)

// If mode is not sent, the default will be "ADDITIVE"
getHarmony(
  color: string | object,
  harmony: 'ANALOGOUS' | 'COMPLEMENTARY' | 'SPLIT_COMPLEMENTARY' | 'TRIADIC' | 'TETRADIC' | 'SQUARE',
  options?: Options
)

// If harmony is not sent, the default will be "COMPLEMENTARY"
getHarmony(
  color: string | object,
  mode: 'ADDITIVE' | 'SUBTRACTIVE',
  options?: Options
)

getHarmony(
  color: string | object,
  harmony: 'ANALOGOUS' | 'COMPLEMENTARY' | 'SPLIT_COMPLEMENTARY' | 'TRIADIC' | 'TETRADIC' | 'SQUARE',
  mode: 'ADDITIVE' | 'SUBTRACTIVE',
  options?: Options
)